SC TO-T

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE TO

Tender Offer Statement under Section 14(d)(1) or 13(e)(1)

of the Securities Exchange Act of 1934

Aventis

(Name of Subject Company (Issuer))

Sanofi-Synthelabo

(Name of Filing Person (Offeror))

Ordinary Shares,

nominal value €3.82 per Ordinary Share

(Title of Class of Securities)

ISIN No. FR0000130460

(CUSIP Number of Class of Securities)

American Depositary Shares

(each representing one Ordinary Share)

(Title of Class of Securities)

053561106

(CUSIP Number of Class of Securities)

John Spinnato

General Counsel, Vice President and Secretary

Sanofi-Synthelabo Inc.

90 Park Avenue

New York, NY 10016

Tel: (212) 551-4000

(Name, Address and Telephone Number of Person Authorized

to Receive Notices and Communications on Behalf of the Filing Person)

Copies to:

Laurent Cohen-Tanugi
Senior Vice President and General Counsel
Sanofi-Synthelabo
174 avenue de France
75013 Paris, France
Tel: + 33 1 53 77 40 00 David A. Katz, Esq.
Wachtell, Lipton, Rosen & Katz
51 West 52nd Street
New York, New York 10019
(212) 403-1000

CALCULATION OF FILING FEE

Transaction Valuation*	Amount of Filing Fee**
$14,449,935,805	$1,830,807

* For purposes of calculating the filing fee only. This amount is based upon the market value of the securities to be acquired in the U.S. Offer and was calculated as the sum of (a) the product of (i) 148,205,509 Aventis ordinary shares, nominal value €3.82 per share, estimated to be held by U.S. holders and (ii) the average of the high and low sales prices of Aventis ordinary shares reported on Euronext Paris on April 5, 2004 (converted into U.S. Dollars on the basis of an exchange rate of €1 = $1.2008, which was the Federal Reserve Bank of New York noon buying rate on that date) and (b) the product of (i) 41,794,491 Aventis American depositary shares estimated to be outstanding and the average of the high and low sales prices of Aventis American depositary shares reported on the New York Stock Exchange on April 5, 2004.

**  The amount of the filing fee, calculated in accordance with Rule 0-11 of the Securities Exchange Act of 1934, equals $126.70 per $1 million of the value of the Aventis ordinary shares subject to the U.S. Offer (including Aventis ordinary shares underlying all of Aventis’s outstanding American depositary shares) proposed to be acquired.

x  Check the box if any part of the fee is offset as provided by Rule 0-11(a)(2) and identify the filing with which the offsetting fee was previously paid. Identify the previous filing by registration statement number, or the Form or Schedule and the date of its filing.

Amount Previously Paid:	$1,373,071	Filing Party:	Sanofi-Synthelabo
Form or Registration No.:	333-112314	Date Filed:	January 29, 2004

o  Check the box if the filing relates solely to preliminary communications made before commencement of a tender offer.

Check the appropriate boxes below to designate any transactions to which this statement relates:

x Third party tender offer subject to Rule 14d-1

o  Issuer tender offer subject to Rule 13e-4

o  Going private transaction subject to Rule 13e-3

o  Amendment to Schedule 13D under Rule 13d-2

Check the following box if the filing is a final amendment reporting the results of the tender offer: o

     This Tender Offer Statement on Schedule TO (this “Schedule TO”) is filed with the United States Securities and Exchange Commission (SEC) by Sanofi-Synthelabo, a French société anonyme, in connection with Sanofi-Synthelabo’s offer to acquire (1) all ordinary shares, nominal value €3.82 per share, of Aventis, a French société anonyme, that are held by holders who are located in the United States and (2) all American Depositary Shares of Aventis (each an “Aventis ADS”, and each Aventis ADS representing one Aventis ordinary share), held by holders wherever located. This offer is being made on the terms and subject to the conditions set forth in the Prospectus, dated April 9, 2004 (the “Prospectus”) attached hereto as Exhibit (a)(4) and incorporated herein by reference, and the related ADS Letter of Transmittal and Form of Acceptance, attached hereto as Exhibits (a)(1)(i) and (a)(1)(vi), respectively, and incorporated herein by reference (collectively, the “U.S. Offer”). Concurrently with the U.S. Offer, Sanofi-Synthelabo is also making, on substantially similar terms and subject to the same conditions: (1) a French offer (the “French Offer”) open to all holders of Aventis ordinary shares who are located in France and to holders of Aventis ordinary shares who are located outside of France, Germany and the United States, if, pursuant to local laws and regulations applicable to such holders, they are permitted to participate in the French Offer; and (2) a German offer (the “German Offer”) open to all holders of Aventis ordinary shares who are located in Germany. Together, the U.S. Offer, the French Offer and the German Offer are being made for all the outstanding ordinary shares of Aventis, including Aventis ordinary shares represented by Aventis ADSs.

Items 1 through 11.

      As permitted by General Instruction F to Schedule TO, all of the information in the Prospectus, attached hereto as Exhibit (a)(4), and the related ADS Letter of Transmittal and Form of Acceptance, attached hereto as Exhibits (a)(1)(i) and (a)(1)(vi), respectively, and any amendment or supplement thereto related to the U.S. Offer hereafter filed with the SEC by Sanofi-Synthelabo, is hereby incorporated herein by reference in answer to Items 1 through 11 of this Schedule TO.

Items 12. Exhibits

(a)(1)(i)	ADS Letter of Transmittal (Aventis ADSs)
(a)(1)(ii)	Notice of Guaranteed Delivery (Aventis ADSs)
(a)(1)(iii)	Letter to Brokers, Dealers, Commercial Banks, Trust Companies and Other Nominees (Aventis ADSs)
(a)(1)(iv)	Letter to Clients from Brokers, Dealers, Commercial Banks, Trust Companies and other Nominees (Aventis ADSs)
(a)(1)(v)	Guidelines for Certification of Taxpayer Indemnification Number on Substitute Form W-9
(a)(1)(vi)	Form of Acceptance for Aventis Ordinary Shares
(a)(1)(vii)	Technical Notice to French Financial Intermediaries and U.S. Custodians (Aventis ordinary shares)
(a)(1)(viii)	Letter to Clients from Brokers, Dealers, Commercial Banks, Trust Companies and other Nominees (Aventis ordinary shares)
(a)(2)	None
(a)(3)	Not applicable
(a)(4)	Prospectus, dated April 9, 2004 (incorporated herein by reference to the filing made by Sanofi-Synthelabo pursuant to Rule 424(b)(5) on April 12, 2004 (File no: 333-112314))
(a)(5)(i)	Press release announcing the offer for Aventis, dated January 26, 2004 (incorporated herein by reference to the filing made by Sanofi-Synthelabo pursuant to Rule 425(a) on January 26, 2004)
(a)(5)(ii)	Press release announcing commencement of U.S. offer , dated April 12, 2004 (incorporated herein by reference to the filing made by Sanofi-Synthelabo pursuant to Rule 425(a) on April 12, 2004)
(a)(5)(iii)	Text of newspaper advertisement dated April 12, 2004 and published in the Wall Street Journal
(b)(1)	Credit Facility Agreement, dated 25 January 2004 (incorporated herein by reference to Exhibit 10.4 to the Registration Statement on Form F-4 filed by Sanofi-Synthelabo (File No. 333-112314))
(d)	None

1

(g)	None
(h)(1)	Opinion of Wachtell, Lipton, Rosen & Katz regarding certain United States federal income tax matters (incorporated herein by reference to Exhibit 8.1 to the Registration Statement on Form F-4 filed by Sanofi-Synthelabo (File No. 333-112314))
(h)(2)	Opinion of Linklaters regarding certain French tax matters (incorporated herein by reference to Exhibit 8.2 to the Registration Statement on Form F-4 filed by Sanofi-Synthelabo (File No. 333-112314))

Item 13. Information Required by Schedule 13e-3.

      Not applicable.

2

SIGNATURE

      After due inquiry and to the best of my knowledge and belief, I certify that the information set forth in this Schedule TO is true, complete and correct.

SANOFI-SYNTHELABO

By:  /s/ JEAN-CLAUDE LEROY

Name: Jean-Claude Leroy

Title:  Senior Vice President — Strategy

April 12, 2004

3

EXHIBIT INDEX

Exhibit
Number	Description
(a)(1)(i)	ADS Letter of Transmittal (Aventis ADSs)
(a)(1)(ii)	Notice of Guaranteed Delivery (Aventis ADSs)
(a)(1)(iii)	Letter to Brokers, Dealers, Commercial Banks, Trust Companies and Other Nominees (Aventis ADSs)
(a)(1)(iv)	Letter to Clients from Brokers, Dealers, Commercial Banks, Trust Companies and other Nominees (Aventis ADSs)
(a)(1)(v)	Guidelines for Certification of Taxpayer Indemnification Number on Substitute Form W-9
(a)(1)(vi)	Form of Acceptance for Aventis Ordinary Shares
(a)(1)(vii)	Technical Notice to French Financial Intermediaries and U.S. Custodians (Aventis ordinary shares)
(a)(1)(viii)	Letter to Clients from Brokers, Dealers, Commercial Banks, Trust Companies and other Nominees (Aventis ordinary shares)
(a)(2)	None
(a)(3)	Not applicable
(a)(4)	Prospectus, dated April 9, 2004 (incorporated herein by reference to the filing made by Sanofi-Synthelabo pursuant to Rule 424(b)(5) on April 12, 2004 (File no: 333-112314))
(a)(5)(i)	Press release announcing the offer for Aventis, dated January 26, 2004 (incorporated herein by reference to the filing made by Sanofi-Synthelabo pursuant to Rule 425(a) on January 26, 2004)
(a)(5)(ii)	Press release announcing commencement of U.S. offer , dated April 12, 2004 (incorporated herein by reference to the filing made by Sanofi-Synthelabo pursuant to Rule 425(a) on April 12, 2004)
(a)(5)(iii)	Text of newspaper advertisement dated April 12, 2004 and published in the Wall Street Journal
(b)(1)	Credit Facility Agreement, dated 25 January 2004 (incorporated herein by reference to Exhibit 10.4 to the Registration Statement on Form F-4 filed by Sanofi-Synthelabo (File No. 333-112314))
(d)	None
(g)	None
(h)(1)	Opinion of Wachtell, Lipton, Rosen & Katz regarding certain United States federal income tax matters (incorporated herein by reference to Exhibit 8.1 to the Registration Statement on Form F-4 filed by Sanofi-Synthelabo (File No. 333-112314))
(h)(2)	Opinion of Linklaters regarding certain French tax matters (incorporated herein by reference to Exhibit 8.2 to the Registration Statement on Form F-4 filed by Sanofi-Synthelabo (File No. 333-112314))

EX-99.A.1.I

Exhibit (a)(1)(i)

      THIS DOCUMENT IS IMPORTANT AND REQUIRES YOUR IMMEDIATE ATTENTION. If you are uncertain about the U.S. offer or about the action you should take, you are recommended to seek your own personal financial advice immediately from an appropriately authorized independent professional advisor.

      If you have sold or otherwise transferred any of your registered holdings of Aventis American depositary shares, please pass a copy of this document and the accompanying prospectus, dated April 9, 2004 (the “prospectus”), as soon as possible to the purchaser or transferee, or to the stockbroker, bank or other agent through whom the sale or transfer was effected, for delivery to the purchaser or transferee. However, the U.S. offer is not being made directly or indirectly in any jurisdiction where prohibited by applicable law and such documents should not be distributed, forwarded or transmitted into or from any jurisdiction where prohibited by applicable law by any means whatsoever including without limitation mail, facsimile, transmission, telex or telephone.

ADS LETTER OF TRANSMITTAL

To Tender American Depositary Shares

of

AVENTIS

(CUSIP: 053561106; ISIN: US0535611067)

Pursuant to the U.S. Offer to Exchange

by

SANOFI-SYNTHELABO

THE U.S. OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 5:00 P.M., NEW YORK CITY TIME, ON MAY 28, 2004, UNLESS THE U.S. OFFER IS EXTENDED.

The U.S. ADS Exchange Agent for the U.S. Offer is:

THE BANK OF NEW YORK

By Mail:	By Hand:	By Overnight Delivery:
The Bank of New York	The Bank of New York	The Bank of New York
Aventis Exchange	Reorganization Services	Aventis Exchange
P.O. Box 859208	101 Barclay Street	161 Bay State Road
Braintree, MA 02185-9208	Receive and Deliver Window, Street Floor	Braintree, MA 02184
	New York, NY 10286

Facsimile Transmission:

(781) 380-3388 (Eligible Institutions Only)

      DELIVERY OF THIS ADS LETTER OF TRANSMITTAL TO AN ADDRESS OTHER THAN AS SET FORTH ABOVE DOES NOT CONSTITUTE A VALID DELIVERY. YOU MUST SIGN THIS ADS LETTER OF TRANSMITTAL WHERE INDICATED BELOW AND COMPLETE THE SUBSTITUTE FORM W-9 PROVIDED BELOW.

      THE INSTRUCTIONS ACCOMPANYING THIS ADS LETTER OF TRANSMITTAL SHOULD BE READ CAREFULLY BEFORE THIS ADS LETTER OF TRANSMITTAL IS COMPLETED.

DESCRIPTION OF AVENTIS AMERICAN DEPOSITARY SHARES (ADSs) TENDERED
Names(s) & Address(es) of Registered Owner(s)
(Please fill in, if blank, exactly as	Aventis ADS(s) Tendered
name(s) appear(s) on certificate(s))	(Attach Additional Signed List, if Necessary)
		Total Number
		of ADSs	Number
	Certificate	Represented by	of ADS(s)
	Number(s)*	Certificate(s)*	Tendered**
		Total Certificated ADSs Tendered
		Total Book ADSs Tendered
		Total ADSs Tendered
* Certificate numbers are not required if tender is made by book-entry transfer.
** If you desire to tender fewer than all Aventis ADSs represented by any certificate listed above, please indicate in this column the number of Aventis ADSs you wish to tender. Otherwise, all Aventis ADSs represented by such certificate will be deemed to have been tendered. See Instruction 4.
IF ANY OF THE CERTIFICATES REPRESENTING AVENTIS ADSs THAT YOU OWN HAVE BEEN LOST, DESTROYED OR MUTILATED, PLEASE FOLLOW THE PROCEDURES SET FORTH IN INSTRUCTION 10.

      This ADS letter of transmittal is to be completed by holders of American depositary shares (“ADSs”) of Aventis, a French société anonyme, if (i) American depositary receipts (“ADRs”) representing the Aventis ADSs are to be forwarded herewith; or (ii) unless an agent’s message is utilized, delivery is to be made by book-entry transfer to the U.S. ADS exchange agent’s account at The Depository Trust Company (the “Book-Entry Transfer Facility”), pursuant to the procedures described in the prospectus, dated April 9, 2004 (the “prospectus”), under “The U.S. Offer — Procedures for Tendering Aventis ADSs”. Delivery of documents to the Book-Entry Transfer Facility in accordance with the Book-Entry Transfer Facility’s procedures does not constitute delivery to the U.S. ADS exchange agent. See Instruction 2.

      Holders whose Aventis ADSs are not immediately available or who cannot deliver the ADRs evidencing their Aventis ADSs and all other documents required hereby to the U.S. ADS exchange agent by the expiration date of the U.S. offer (as defined below), or who cannot comply with the book-entry transfer procedures on a timely basis, may nevertheless tender their Aventis ADSs pursuant to the guaranteed delivery procedures described in the prospectus under “The U.S. Offer — Procedures for Tendering Aventis ADSs — Guaranteed delivery”.

      Acceptance of the U.S. offer in respect of Aventis ordinary shares (except insofar as they are represented by Aventis ADSs) cannot be made by means of this ADS letter of transmittal. If you directly hold Aventis ordinary shares, you may obtain a form of acceptance from MacKenzie Partners, Inc., the information agent, or contact your French financial intermediary or your U.S. custodian, as the case may be. See Instruction 11 of this ADS letter of transmittal.

      Your bank or broker can assist you in completing this ADS letter of transmittal. The instructions included with this letter of transmittal must be followed. Questions and requests for assistance or for additional copies of the prospectus and this ADS letter of transmittal may be directed to MacKenzie Partners, Inc., the information agent, at the address and telephone numbers indicated below.

      If delivery of Aventis ADSs is to be made by book-entry transfer to an account maintained by the U.S. ADS exchange agent at The Book-Entry Transfer Facility, then either this ADS letter of transmittal or an agent’s message should be used. The term “agent’s message” means a message which is transmitted by the Book-Entry Transfer Facility to and received by the U.S. ADS exchange agent and which forms a part of a book-entry confirmation. This message must state that the Book-Entry Transfer Facility has received an express acknowledgment from a participant in the Book-Entry Transfer Facility’s

2

system that (i) the participant is tendering Aventis ADSs that are the subject of a confirmation of a book-entry transfer, (ii) the participant has received and agrees to be bound by the applicable letter of transmittal, and (iii) Sanofi-Synthelabo and the U.S. ADS exchange agent may enforce the agreement against the participant.

o CHECK HERE IF AVENTIS ADSs ARE BEING DELIVERED BY BOOK-ENTRY TRANSFER MADE TO AN ACCOUNT MAINTAINED BY THE U.S. ADS EXCHANGE AGENT WITH THE BOOK-ENTRY TRANSFER FACILITY AND COMPLETE THE FOLLOWING:

Name of Tendering Institution:

Account Number:

Transaction Code Number:

o CHECK HERE IF AVENTIS ADSs ARE BEING DELIVERED PURSUANT TO A NOTICE OF GUARANTEED DELIVERY PREVIOUSLY SENT TO THE U.S. ADS EXCHANGE AGENT. ENCLOSE A COPY OF SUCH NOTICE OF GUARANTEED DELIVERY AND COMPLETE THE FOLLOWING:

Name(s) of Registered Owner(s):

Date of Execution of Notice of Guaranteed Delivery:

Window Ticket Number (if any):

Name of Institution That Guaranteed Delivery:

If Delivered by Book-Entry Transfer to the Book-Entry Transfer Facility, check here: o

Account Number:

Transaction Code Number:

      Receipt of a notice of guaranteed delivery will not be treated as a valid acceptance for purposes of satisfying the minimum tender condition set forth in the prospectus under “The U.S. Offer — Conditions to the U.S. Offer — Minimum tender condition”, unless the Aventis ADSs referred to in the notice of guaranteed delivery are received by the U.S. ADS exchange agent prior to the expiration of the guarantee period.

3

NOTE: SIGNATURE(S) MUST BE PROVIDED BELOW.

PLEASE READ THE INSTRUCTIONS SET FORTH IN THIS ADS LETTER OF TRANSMITTAL

CAREFULLY.

Ladies and Gentlemen:

      The undersigned hereby tenders to Sanofi-Synthelabo, a French société anonyme, the above-described American depositary shares (“ADSs”) of Aventis, a French société anonyme, pursuant to Sanofi-Synthelabo’s offer to exchange each outstanding Aventis ADS for 1.6667 Sanofi-Synthelabo ADSs (each Sanofi-Synthelabo ADS representing one-half of one Sanofi-Synthelabo ordinary share) and an amount in cash in U.S. dollars equal to €11.50, without interest (the “standard entitlement”), upon the terms and subject to the conditions set forth in the prospectus, dated April 9, 2004 (the “prospectus”), receipt of which is hereby acknowledged, and in this ADS letter of transmittal (which, together with the prospectus, and any amendments or supplements hereto or thereto, collectively constitute the “U.S. offer”). The U.S. offer is being made in connection with Sanofi-Synthelabo’s offer to acquire all of the outstanding Aventis ordinary shares, including Aventis ordinary shares represented by Aventis ADSs.

      The U.S. offer contains a mix and match election feature that allows the undersigned to elect to receive for each tendered Aventis ADS, in lieu of the standard entitlement:

•  2.0588 Sanofi-Synthelabo ADSs; or

•  an amount in U.S. dollars equal to €60.43, in cash, without interest.

      The undersigned is not required to make any election (in which case the undersigned shall automatically receive the standard entitlement) or to make the same election for all of the Aventis ADSs that the undersigned tenders in the U.S. offer. The undersigned understands that the mix and match elections are subject to proration and allocation adjustments that will ensure that, in the aggregate (and subject to adjustment if Aventis pays any dividend or interim dividend before the settlement of the offers), 81.0% of the Aventis ordinary shares (including Aventis ordinary shares represented by Aventis ADSs) tendered in the U.S. offer and the concurrent French offer and German offer will be exchanged for Sanofi-Synthelabo ordinary shares (including Sanofi-Synthelabo ordinary shares represented by Sanofi-Synthelabo ADSs) and 19.0% will be purchased for cash. The undersigned acknowledges that, if it makes a mix and match election, it will not be informed of the exact number of Sanofi-Synthelabo ADSs or the amount of cash that it shall receive until settlement of the consideration under the U.S. offer. The undersigned also acknowledges that, if it does not properly complete and submit its mix and match election pursuant to this ADS letter of transmittal, or if there are any errors or mistakes in completing the “Mix and Match Election” box, including errors in the number of eligible elections that can be made with respect to the tendered Aventis ADSs, Sanofi-Synthelabo shall be able to determine, in its sole discretion, that any such tendered Aventis ADSs shall receive the standard entitlement.

      The undersigned acknowledges that, if Aventis pays any dividend or any interim dividend in respect of the Aventis ordinary shares, including Aventis ordinary shares represented by Aventis ADSs, before the settlement of the offers, the consideration offered in exchange for each Aventis ordinary share and each Aventis ADS tendered will be reduced by an amount equal to the net value of the dividend paid per Aventis ordinary share in the manner described in the prospectus under “The U.S. Offer — Consideration Offered after Payment of Aventis Dividends”. In respect of any Sanofi-Synthelabo ADSs that a holder receives in exchange for Aventis ADSs that the undersigned tenders in the offers, the undersigned shall be entitled to receive any annual dividend with respect to Sanofi-Synthelabo’s 2003 results that is declared on the Sanofi-Synthelabo ordinary shares and any other dividend that is paid after the settlement of this exchange offer.

      The undersigned hereby instructs the U.S. ADS exchange agent to accept the U.S. offer on behalf of the undersigned with respect to the Aventis ADSs (which expression in this ADS letter of transmittal shall, except where the context otherwise requires, be deemed to include, without limitation, the Aventis ordinary shares represented thereby) delivered herewith.

      Subject to, and effective upon, acceptance for payment for the Aventis ADSs tendered herewith, in accordance with the terms of the U.S. offer, the undersigned hereby sells, assigns and transfers to, or upon the order of, Sanofi-Synthelabo all right, title and interest in and to all the Aventis ADSs being tendered hereby (and any and all other Aventis ordinary shares or other securities issued or issuable in respect thereof) and all dividends, distributions (including, without limitation, distributions of additional Aventis ADSs or Aventis ordinary shares) and rights declared, paid or distributed in respect of such shares or securities on or after the settlement date of the U.S. offer (collectively, “distributions”) and irrevocably appoints The Bank of New York, as the U.S. ADS exchange agent, the true and lawful agent and attorney-in-fact of the undersigned,

4

with full knowledge that the U.S. ADS exchange agent is also acting as the agent of Sanofi-Synthelabo in connection with the U.S. offer, with respect to such Aventis ADSs and the distributions, with full power of substitution (such power of attorney being deemed to be an irrevocable power coupled with an interest), (a) to have the ADRs evidencing the Aventis ADSs and any distributions delivered to the U.S. ADS exchange agent or, if tender is by book-entry transfer, transfer Aventis ADSs and any distributions to the account of the U.S. ADS exchange agent at The Depository Trust Company (hereinafter referred to as the “Book-Entry Transfer Facility”), together, in any such case, with all accompanying evidences of transfer and authenticity to the U.S. ADS exchange agent or upon the order of the U.S. ADS exchange agent, in each case, acting upon the instruction of Sanofi-Synthelabo, (b) to surrender such Aventis ADSs for the purpose of withdrawal of the underlying Aventis ordinary shares in accordance with the deposit agreement, (c) to instruct the depositary of the Aventis ADS facility to deliver the certificates evidencing the Aventis ordinary shares underlying the Aventis ADSs, or transfer ownership of such Aventis ordinary shares underlying the Aventis ADSs on the account books maintained with respect to the Aventis ordinary shares, together, in any such case, with all accompanying evidences of transfer and authenticity, to or upon the order of Sanofi-Synthelabo, (d) to combine the undersigned’s fractional entitlements to shares of Sanofi-Synthelabo ADSs with other fractional entitlements and sell them on the New York Stock Exchange, (e) to tender, or to cause to be tendered, the Aventis ordinary shares underlying the tendered Aventis ADSs as part of the French centralizing procedures as soon as practicable after the expiration of the offer period, and (f) to receive all benefits and otherwise exercise all rights of beneficial ownership of such Aventis ADSs (and all such other Aventis ordinary shares or securities) and any distributions, all in accordance with the terms and conditions of the U.S. offer. The undersigned agrees that Sanofi-Synthelabo may instruct the U.S. ADS exchange agent to take the actions specified in clauses (a), (b), (c) or (e) above prior to acceptance by Sanofi-Synthelabo of those Aventis ADSs for exchange in the U.S. offer. Sanofi-Synthelabo shall not have the rights specified in clauses (d) or (f) above until it has irrevocably accepted those Aventis ADSs tendered in the offers. Upon acceptance by Sanofi-Synthelabo of tendered Aventis ADSs in the U.S. offer, the undersigned shall have no further rights with respect to those Aventis ADSs, except that the undersigned shall have a right to receive from Sanofi-Synthelabo the offer consideration in accordance with the U.S. offer.

      The undersigned hereby irrevocably appoints each designee of Sanofi-Synthelabo as the attorney-in-fact and proxy of the undersigned, each with full power of substitution, to exercise all voting and other rights of the undersigned in such manner as each such attorney and proxy or his substitute shall, in his sole discretion, deem proper and otherwise act (by written consent or otherwise), with respect to all of the Aventis ADSs tendered hereby (and any associated distributions) that have been accepted for payment by Sanofi-Synthelabo prior to the time of any vote or other action (and any and all other Aventis ordinary shares or other securities or rights issued or issuable in respect of such Aventis ADSs) at any meeting of securityholders of Aventis (whether annual or special and whether or not an adjourned or postponed meeting), any actions by written consent in lieu of any such meeting or otherwise. This proxy and power of attorney is coupled with an interest in the tendered Aventis ADSs, is irrevocable and is granted in consideration of, and is effective upon, the acceptance for payment of the Aventis ADSs by Sanofi-Synthelabo in accordance with the terms of the U.S. offer. Such acceptance for payment shall revoke any other proxy or written consent granted by the undersigned at any time with respect to such Aventis ADSs (and all such other Aventis ordinary shares or other securities or rights), and no subsequent proxies will be given or written consents will be executed by the undersigned (and if given or executed, will not be deemed effective). The undersigned understands that, in order for the Aventis ADSs to be deemed validly tendered, immediately upon Sanofi-Synthelabo’s acceptance of such Aventis ADSs, Sanofi-Synthelabo or its designee must be able to exercise full voting, consent and other rights with respect to such Aventis ADSs (and any associated distributions), including, the right to instruct the ADS depositary with respect to voting at any meeting of Aventis’s stockholders.

      The undersigned hereby represents and warrants that the undersigned has full power and authority to accept the U.S. offer and to tender, exchange, sell, assign, cancel and transfer the Aventis ADSs (and any associated distributions) tendered hereby (and any and all other Aventis ordinary shares or other securities or rights issued or issuable in respect of such Aventis ADSs), and that when the same are accepted for payment by Sanofi-Synthelabo, Sanofi-Synthelabo will acquire good, marketable and unencumbered title thereto and to all distributions, free and clear of all liens, restrictions, charges and encumbrances and not subject to any adverse claims.

      The undersigned, upon request, shall execute and deliver all additional documents deemed by the U.S. ADS exchange agent or Sanofi-Synthelabo to be necessary or desirable to complete the sale, assignment, transfer of the Aventis ADSs (and any associated distributions) tendered hereby (and any and all other Aventis ordinary shares or other securities or rights issued or issuable in respect of such Aventis ADSs).

5

      No authority herein conferred or agreed to be conferred shall be affected by, and all such authority shall survive, the death or incapacity of the undersigned. All obligations of the undersigned hereunder shall be binding upon the heirs, personal representatives, successors and assigns of the undersigned. Except as stated in the prospectus, this tender is irrevocable.

      The undersigned understands that the valid tender of the Aventis ADSs pursuant the procedures described in the prospectus under “The U.S. Offer — Procedures for Tendering Aventis ADSs”, and the instructions hereto, will constitute a binding agreement between the undersigned and Sanofi-Synthelabo upon the terms and subject to the conditions of the U.S. offer. Without limiting the foregoing, if the price to be paid in the U.S. offer is amended in accordance with the U.S. offer, the price to be paid to the undersigned will be the amended price notwithstanding the fact that a different price is stated in this ADS letter of transmittal. The undersigned recognizes that under certain circumstances set forth in the prospectus, Sanofi-Synthelabo may not be required to accept for payment any of the Aventis ADSs tendered hereby. If acceptance has been made in respect of Aventis ADSs, then a separate acceptance in respect of Aventis ordinary shares represented by such Aventis ADSs may not be made.

      The undersigned understands that Sanofi-Synthelabo will not issue any fraction of a Sanofi-Synthelabo ADS. Instead, each holder tendering Aventis ADSs who would otherwise be entitled to a fraction of a Sanofi-Synthelabo ADS, after combining all fractional Sanofi-Synthelabo ADSs to which the stockholder would otherwise be entitled, will receive cash in an amount equal to the product of that fraction and the average sale price per Sanofi-Synthelabo ADS, net of expenses, realized on the New York Stock Exchange in the sale by the U.S. ADS exchange agent of all the aggregated fractional Sanofi-Synthelabo ADSs that would have otherwise been issued in the offers. The sale of the aggregated Sanofi-Synthelabo ADSs on the New York Stock Exchange will occur no later than six trading days following the settlement of the offers. Payment of cash in lieu of any fractional Sanofi-Synthelabo ADS that a holder would otherwise have been entitled to receive pursuant to the terms of the U.S. offer will be paid to such holder as promptly as practicable.

      Unless otherwise indicated herein in the box entitled “Special Issuance Instructions,” in consideration of the Aventis ADSs tendered hereby, the undersigned hereby instructs the U.S. ADS exchange agent to issue a check (including any cash payments for the Aventis ADSs and cash in lieu of fractional Sanofi-Synthelabo ADSs, if any) and one certificate evidencing the applicable number of Sanofi-Synthelabo ADSs (or, in the case of delivery through the Book-Entry Transfer Facility, credit the appropriate account with the cash and Sanofi-Synthelabo ADSs), and return all Aventis ADRs representing Aventis ADSs not purchased or not tendered, in the name(s) of the undersigned. Similarly, unless otherwise indicated in the box entitled “Special Delivery Instructions,” the undersigned hereby instructs the U.S. ADS exchange agent to mail the certificate representing Sanofi-Synthelabo ADSs and the check (or, in the case of delivery through the Book-Entry Transfer Facility, credit the appropriate account with the cash and Sanofi-Synthelabo ADSs), and return any ADRs representing Aventis ADSs not purchased or tendered (and accompanying documents, as appropriate), to the undersigned at the address(es) appearing above in the box entitled “Description of Aventis American Depositary Shares (ADSs) Tendered”. In the case of a book-entry delivery of Aventis ADSs, the undersigned hereby instructs the U.S. ADS exchange agent to credit the account maintained at the Book-Entry Transfer Facility with any Aventis ADSs that are not tendered or are not accepted for exchange.

      In the event that the boxes entitled “Special Issuance Instructions” and “Special Delivery Instruction” are both completed, the undersigned hereby instructs the U.S. ADS exchange agent to issue the check and register the Sanofi-Synthelabo ADSs, and return all Aventis ADSs not purchased or not tendered, in the name(s) of, and mail such check and certificates to, the person(s) so indicated. Unless otherwise indicated herein in the box entitled “Special Issuance Instructions,” the undersigned hereby instructs the U.S. ADS exchange agent to credit any Aventis ADSs tendered hereby and delivered by book-entry transfer, but which are not purchased, by crediting the account at the Book-Entry Transfer Facility. The undersigned recognizes that Sanofi-Synthelabo has no obligation, pursuant to the Special Issuance Instructions, to transfer any Aventis ADSs from the name of the registered owner(s) thereof if Sanofi-Synthelabo does not purchase any of the Aventis ADSs tendered hereby.

      The cash consideration paid to tendering Aventis ADS holders will be paid in U.S. dollars converted at a then-current spot exchange rate and distributed, net of expenses, to such holders. For further information see “The U.S. Offer” in the prospectus. Under no circumstances will interest be paid in respect of the exchange of cash and Sanofi-Synthelabo ADSs for Aventis ADSs tendered, regardless of any delay in making the exchange.

      The undersigned understands that Sanofi-Synthelabo reserves the right to transfer or assign, in whole at any time, or in part from time to time, to one or more of its affiliates, the right to purchase all or any portion of the Aventis ADSs tendered pursuant to the U.S. offer, but any such transfer or assignment will not relieve Sanofi-Synthelabo of its obligations under the

6

U.S. offer and will in no way prejudice the rights of holders to receive payment for Aventis ADSs validly tendered and accepted for payment pursuant to the U.S. offer.

      SUBJECT TO THE TERMS OF THE PROSPECTUS, THIS ADS LETTER OF TRANSMITTAL SHALL NOT BE CONSIDERED COMPLETE AND VALID, AND DELIVERY OF AVENTIS ADSs PURSUANT TO THE U.S. OFFER SHALL NOT BE MADE, UNTIL THE AVENTIS ADSs IN RESPECT OF WHICH THE U.S. OFFER IS BEING ACCEPTED AND ALL OTHER REQUIRED DOCUMENTATION HAVE BEEN RECEIVED BY THE U.S. ADS EXCHANGE AGENT. SANOFI-SYNTHELABO WILL DETERMINE IN ITS SOLE DISCRETION ALL QUESTIONS AS TO THE FORM OF DOCUMENTS, INCLUDING ANY NOTICE OF WITHDRAWAL AND THE VALIDITY, ELIGIBILITY (INCLUDING TIME OF RECEIPT) AND ACCEPTANCE OF TENDERED AVENTIS ADSs. SANOFI-SYNTHELABO’S DETERMINATION WILL BE FINAL AND BINDING ON ALL PARTIES.

7

SPECIAL ISSUANCE INSTRUCTIONS

(See Instructions 5 and 7)

   To be completed ONLY if the check and/or Sanofi-Synthelabo ADSs with respect to the Aventis ADSs accepted for exchange are to be issued in the name of and sent to someone other than the undersigned.

Issue     o Check and/or     o Certificates to:

Name:

(Please Print)

Address:

(Include Zip Code)

(Taxpayer Identification or Social Security No.)

(also complete Substitute Form W-9 below)

SPECIAL DELIVERY INSTRUCTIONS

(See Instructions 5 and 7)

   To be completed ONLY if the ADRs for Aventis ADSs not tendered or not purchased, and/or the check and Sanofi-Synthelabo ADSs with respect to the Aventis ADSs accepted for exchange, are to be sent to someone other than the undersigned, or to the undersigned at an address other than that shown in the “Special Issuance Instructions”.

Mail     o Check and/or     o Certificates to:

Name:

(Please Print)

Address:

(Include Zip Code)

(Taxpayer Identification or Social Security No.)

MIX AND MATCH ELECTION
(Complete only if you would like to exercise the mix and match election.)
(See Instruction 14)
1	Enter the number of Aventis ADSs for which you would like to make a mix and match election. Note: You must also complete Box 2A and/or Box 2B if you make this election. In addition, the number in Box 1 must be less than or equal to the total number of Aventis ADSs tendered.	1
2A	Enter the number of Aventis ADSs for which you would like to make the All Stock Election.	2A
2B	Enter the number of Aventis ADSs for which you would like to make the All Cash Election. Note: The sum of the number in Box 2A and the number in Box 2B must equal the number in Box 1.	2B

8

SIGN HERE

(AND PLEASE COMPLETE SUBSTITUTE FORM W-9)

Signature(s) of Holder(s)

Dated: ______________________________ , 2004

(Must be signed by registered owner(s) exactly as name(s) appear(s) on the ADR representing the Aventis ADS or on a security position listing or by person(s) authorized to become registered owner(s) by endorsements, stock powers and documents transmitted herewith. If a signature is by an officer on behalf of a corporation or by an executor, administrator, trustee, guardian, attorney-in-fact, agent or other person acting in a fiduciary or representative capacity, please provide the following information. See Instructions 1 and 5.)

Name(s):

(Please Print)

Name of Firm:

Capacity (full title):

Address:

(Zip Code)

(Area Code) Telephone Number:

Taxpayer Identification or
Social Security No.:

(See Substitute Form W-9)

GUARANTEE OF SIGNATURE(S)

(IF REQUIRED — SEE INSTRUCTIONS 1 AND 5)

Authorized Signature:

Name:

(Please Print)

Name of Firm:

Address:

(Zip Code)

(Area Code) Telephone Number:

Dated: ______________________________ , 2004

9

INSTRUCTIONS

FORMING A PART OF THE TERMS AND CONDITIONS OF THE U.S. OFFER

      To complete this ADS letter of transmittal, you must do the following:

•  Fill in the box entitled “Description of Aventis American Depositary Shares (ADSs) Tendered”.

•  Sign and date this ADS letter of transmittal in the box entitled “Sign Here”.

•  Fill in and sign in the box entitled “Substitute Form W-9”.

      In completing this ADS letter of transmittal, you may (but are not required to) also do the following:

•  If you want any cash payment and/or Sanofi-Synthelabo ADSs issued in the name of another person, complete the box entitled “Special Issuance Instructions”.

•  If you want any cash payment and/or Sanofi-Synthelabo ADSs, or ADRs for Aventis ADSs not tendered or purchased, delivered to an address other than that appearing under your signature, complete the box entitled “Special Delivery Instructions”.

      If you complete the box entitled “Special Issuance Instructions” or “Special Delivery Instructions,” you must have your signature guaranteed by an Eligible Institution (as defined in Instruction 1 below) unless the ADS letter of transmittal is signed by an Eligible Institution.

      1. Guarantee of Signatures. All signatures on this ADS letter of transmittal must be guaranteed by a bank, broker, dealer, credit union, savings association or other entity that is a member in good standing of the Securities Transfer Agents Medallion Program (an “Eligible Institution”), unless (i) this ADS letter of transmittal is signed by the registered owner(s) (which term, for purposes of this document, shall include any participant in the Book-Entry Transfer Facility whose name appears on a security position listing as the owner of Aventis ADSs) of the Aventis ADSs tendered hereby and such holder(s) has not completed either the box entitled “Special Issuance Instructions” or the box entitled “Special Delivery Instructions” herein or (ii) such Aventis ADSs are tendered for the account of an Eligible Institution. See Instruction 5.

      2. Delivery of ADS Letter of Transmittal and ADRs or Book-Entry Confirmations. This ADS letter of transmittal is to be used either if (i) ADRs evidencing the Aventis ADSs for the U.S. offer are to be forwarded herewith or (ii) unless an agent’s message (as defined below) is used, if Aventis ADSs are to be delivered by book-entry transfer pursuant to the procedure set forth in the prospectus under “The U.S. Offer —Procedure for Tendering Aventis ADSs”. ADRs evidencing all physically tendered Aventis ADSs, or confirmation of a book-entry transfer, if such procedure is available, into the U.S. ADS exchange agent’s account at the Book-Entry Transfer Facility (“Book-Entry Confirmation”) of all Aventis ADSs delivered by book-entry transfer together with a properly completed and duly executed ADS letter of transmittal (or facsimile thereof), or an agent’s message in the case of book-entry transfer, and any other documents required by this ADS letter of transmittal, must be received by the U.S. ADS exchange agent at one of its addresses set forth herein prior to the expiration date of the U.S. offer. If ADRs evidencing tendered Aventis ADSs are forwarded to the U.S. ADS exchange agent in multiple deliveries, a properly completed and duly executed ADS letter of transmittal must accompany each such delivery.

      The term “agent’s message” means a message, transmitted by the Book-Entry Transfer Facility to, and received by, the U.S. ADS exchange agent and forming a part of the Book-Entry Confirmation, which states that the Book-Entry Transfer Facility has received an express acknowledgment from the participants in the Book-Entry Transfer Facility tendering the Aventis ADSs that such participant has received this ADS letter of transmittal and agrees to be bound by the terms of this ADS letter of transmittal and that Sanofi-Synthelabo may enforce such agreement against such participant.

      Holders whose ADRs evidencing their tendered Aventis ADSs are not immediately available or who cannot deliver all other required documents to the U.S. ADS exchange agent on or prior to the expiration date for the U.S. offer, or who cannot comply with the procedures for book-entry transfer on a timely basis, may nevertheless tender their Aventis ADSs by properly completing and duly executing a notice of guaranteed delivery pursuant to the guaranteed delivery procedure set forth in the prospectus under “The U.S. Offer — Procedures for Tendering Aventis ADSs — Guaranteed delivery”. Pursuant to such procedure: (i) such tender must be made by or through

10

an eligible institution; (ii) a properly completed and duly executed notice of guaranteed delivery substantially in the form provided by Sanofi-Synthelabo must be received by the U.S. ADS exchange agent prior to the expiration date for the U.S. offer; and (iii) ADRs evidencing such tendered Aventis ADSs or confirmation of the book-entry transfer of such Aventis ADSs into the U.S. ADS exchange agent’s account at the Book-Entry Transfer Facility, as well as a ADS letter of transmittal, properly completed and duly executed with any required signature guarantees (or, in the case of a book-entry transfer, an agent’s message), and all other documents required by this ADS letter of transmittal, must be received by the U.S. ADS exchange agent within three New York Stock Exchange trading days after the date of execution of such notice of guaranteed delivery.

      The method of delivery of this ADS letter of transmittal, ADRs evidencing Aventis ADSs and all other required documents, including delivery through the Book-Entry Transfer Facility, is at the option and risk of the tendering ADS holder, and the delivery will be deemed made only when actually received by the U.S. ADS exchange agent (including, in the case of a book-entry transfer, by Book-Entry Confirmation). If delivery is by mail, registered mail with return receipt requested, properly insured, is recommended. In all cases, sufficient time should be allowed to ensure timely delivery.

      No alternative, conditional or contingent tenders will be accepted, and no fractional Aventis ADSs will be purchased or accepted for exchange. By execution of this ADS letter of transmittal (or facsimile hereof), all tendering holders of Aventis ADSs waive any right to receive any notice of the acceptance of their Aventis ADSs for exchange.

      3. Inadequate Space. If the space provided herein under “Description of Aventis American Depositary Shares (ADSs) Tendered” is inadequate, the certificate numbers, the number of Aventis ADSs represented by such certificates and the number of Aventis ADSs tendered should be listed on a separate schedule and attached hereto.

      4. Partial Tenders (Not Applicable to ADS Holders who Tender by Book-Entry Transfer). If fewer than all of the Aventis ADSs represented by the ADRs delivered herewith to the U.S. ADS exchange agent are to be tendered, fill in the number of Aventis ADSs that are to be tendered in the box entitled “Number of Aventis ADSs Tendered”. In such cases, new certificate(s) representing the remainder of the Aventis ADSs that were represented by ADRs will be sent to the registered owner, unless otherwise provided in the box entitled “Special Delivery Instructions” herein as soon as practicable after the expiration or termination of the U.S. offer. All Aventis ADSs represented by ADRs delivered to the U.S. ADS exchange agent will be deemed to have been tendered unless otherwise indicated. In the case of partial acceptances, Aventis ADSs in respect of which the U.S. offer was not accept will not be reissued to a person other than the registered owner.

      5. Signatures on ADS Letter of Transmittal, Stock Powers and Endorsements. If this ADS letter of transmittal is signed by the registered owner(s) of the Aventis ADSs tendered hereby, the signature(s) must correspond with the name(s) as written on the face of the ADR evidencing such Aventis ADSs without alteration, enlargement or any other change whatsoever.

      If any Aventis ADS tendered hereby is owned of record by two or more persons, all such persons must sign this ADS letter of transmittal.

      If any of the tendered Aventis ADSs are registered in the names of different holders, it will be necessary to complete, sign and submit as many separate ADS letters of transmittal as there are different registrations of such Aventis ADSs.

      If this ADS letter of transmittal is signed by the registered owner(s) of the Aventis ADSs tendered hereby, no endorsements of certificates or separate stock powers are required, unless payment is to be made to, or ADRs for Aventis ADSs not tendered or not exchanged are to be issued in the name of, a person other than the registered owner(s), in which case, the certificate(s) representing the Aventis ADSs tendered hereby must be endorsed or accompanied by appropriate stock powers, in either case signed exactly as the name(s) of the registered owner(s) appear on such certificate(s). Signatures on such certificate(s) and stock powers must be guaranteed by an Eligible Institution.

      If this ADS letter of transmittal is signed by a person other than the registered owner(s) of the Aventis ADSs tendered hereby, the certificate(s) representing the Aventis ADSs tendered hereby must be endorsed or accompanied by appropriate stock powers, in either case signed exactly as the name(s) of the registered owner(s)

11

appear(s) on such certificate(s). Signatures on such certificate(s) and stock powers must be guaranteed by an Eligible Institution.

      If this ADS letter of transmittal or any certificate or stock power is signed by a trustee, executor, administrator, guardian, attorney-in-fact, officer of a corporation or other person acting in a fiduciary or representative capacity, such person should so indicate when signing, and proper evidence satisfactory to Purchaser of such person’s authority to so act must be submitted.

      6. Stock Transfer Taxes. Sanofi-Synthelabo will pay or cause to be paid any transfer taxes with respect to the exchange of Aventis ADSs not based on income. If, however, a transfer tax is imposed based on income or for any reason other than the exchange of securities in the U.S. offer, then those transfer taxes, whether imposed on the registered holder or any other persons, will not be payable to the tendering holder.

      Except as provided in this Instruction 6, it will not be necessary for transfer tax stamps to be affixed to the ADRs evidencing the Aventis ADSs listed in this ADS letter of transmittal.

      7. Special Issuance and Delivery Instructions. If the check and/or Sanofi-Synthelabo ADSs exchanged for tendered Aventis ADSs are to be issued or delivered, or ADRs evidencing Aventis ADSs not tendered or exchanged pursuant to the U.S. offer are to be sent, to someone other than the person(s) signing this ADS letter of transmittal or to the person(s) signing this ADS letter of transmittal but at an address other than that shown in the box entitled “Description of Aventis American Depositary Shares (ADSs) Tendered” herein, the appropriate boxes in this ADS letter of transmittal must be completed.

      8. Requests for Assistance or Additional Copies. Questions and requests for assistance or for additional copies of the prospectus, the ADS letter of transmittal and the notice of guaranteed delivery, may be directed to the information agent at its respective telephone numbers and location set forth below. You may also contact your broker, dealer, commercial bank, trust company or other nominee for assistance concerning the U.S. offer.

      9. Conditions; Waiver of Conditions. Sanofi-Synthelabo’s obligation to accept Aventis ADSs in the U.S. offer is subject to the conditions set forth in the prospectus. Such conditions, however, may be waived, in whole or in part, by Sanofi-Synthelabo, in its sole discretion, at any time and from time to time, in the case of any Aventis ADSs tendered. See “The U.S. Offer — Conditions to the U.S. Offer” in the prospectus.

      10. Lost, Destroyed or Stolen Certificates. If any ADR representing Aventis ADSs has been lost, destroyed or stolen, the holder(s) should promptly notify Citibank, as depositary, in order to obtain a replacement ADR(s). This ADS letter of transmittal and related documents cannot be processed until the procedures for replacing mutilated, lost, destroyed or stolen ADRs evidencing Aventis ADSs have been followed.

      11. Holders of Aventis Ordinary Shares Not Represented by Aventis ADSs. Holders of Aventis ordinary shares have been sent a form of acceptance instruction form with the prospectus and may not accept the U.S. offer in respect of such Aventis ordinary shares pursuant to this ADS letter of transmittal, except insofar as those Aventis ordinary shares are represented by Aventis ADSs. If any holder of Aventis ordinary shares that are not represented by Aventis ADSs needs to obtain a copy of a form of acceptance instruction form, such holder should contact MacKenzie Partners, Inc., as information agent, at the appropriate address and telephone number set forth in the prospectus.

      12. No Interest; Foreign Exchange Currency. Under no circumstances will interest be paid on the exchange of Aventis ADSs tendered for Sanofi-Synthelabo ADSs and cash, regardless of any delay in making the exchange or extension of the expiration date for the U.S. offer. The cash consideration for tendering holders of Aventis ADSs will be paid in U.S. dollars, converted at a then-current spot exchange rate, and will be distributed, net of expenses, to such holders. For further information, see “The U.S. Offer” in the prospectus.

      13. Expiration Date. The expiration date will be 5:00 p.m., New York City time, on May 28, 2004, unless: (a) the French Autorité des marchés financiers (“AMF”) sets a later expiration date for the tender period of the French offer, (b) the AMF has not set an expiration date for the French offer by May 28, 2004, (c) the AMF subsequently extends the tender period of the French offer, or (d) the offers lapse or are withdrawn prior to that time. Sanofi-Synthelabo intends that the U.S. offer, the French offer and the German offer will expire simultaneously. If the initial expiration date of the French offer is later than May 28, 2004, or if the French offer

12

period is extended, Sanofi-Synthelabo will issue a press release announcing a corresponding extension of the U.S. offer.

      14. Mix and Match Election. For each of your tendered Aventis ADSs, you may elect to receive either all Sanofi-Synthelabo ADSs or all cash, instead of the standard entitlement (which consists of 1.6667 Sanofi-Synthelabo ADSs and an amount in cash in U.S. dollars equal to €11.50, without interest for each tendered Aventis ADS). Specifically, the mix and match election feature allows you to elect to receive for each of your tendered Aventis ADSs, in lieu of the standard entitlement described above:

•  2.0588 Sanofi-Synthelabo ADSs (the “All Stock Election”); or

•  an amount in U.S. dollars equal to €60.43 in cash, without interest (the “All Cash Election”).

      You are not required to make any election (in which case you will automatically receive the standard entitlement) or make the same election for all of the Aventis ADSs that you tender. The mix and match elections, however, are subject to proration and allocation adjustments that will ensure that, in the aggregate, 81.0% of the Aventis ordinary shares (including Aventis ordinary shares underlying the Aventis ADSs) tendered in the U.S. offer and the concurrent French offer and German offer will be exchanged for Sanofi-Synthelabo ordinary shares (including Sanofi-Synthelabo ordinary shares underlying Sanofi-Synthelabo ADSs) and 19.0% will be purchased for cash. For additional information regarding the proration and allocation adjustments, see the prospectus under “The U.S. Offer — Mix and Match Election”.

      To make an All Stock Election or an All Cash Election with respect to any of your tendered Aventis ADSs, you must provide the information requested above in the box entitled “Mix and Match Election”. If there are any errors or mistakes in completing the “Mix and Match Election” box, including errors in the number of eligible elections that can be made with respect to the tendered Aventis ADSs, Sanofi-Synthelabo shall be able to determine, in its sole discretion, that any such tendered Aventis ADSs shall receive the standard entitlement.

      If you hold Aventis ADSs in book-entry form and plan to tender Aventis ADSs using an agent’s message, you should indicate your mix and match election as part of the agent’s message.

      15. Consideration Offered after Payment of Dividends. If Aventis pays any dividend or any interim dividend in respect of the Aventis ordinary shares, including Aventis ordinary shares represented by Aventis ADSs, before the settlement of the offers, the consideration offered in exchange for each Aventis ADS tendered will be reduced by an amount equal to the net value of the dividend paid per Aventis ordinary share in the manner described under “The U.S. Offer — Consideration Offered after Payment of Aventis Dividends”.

      In respect of Sanofi-Synthelabo ordinary shares, including Sanofi-Synthelabo ordinary shares represented by Sanofi-Synthelabo ADSs, issued in exchange or part exchange for your tendered Aventis securities, you will be entitled to receive:

•  any annual dividend that is approved to be paid on the Sanofi-Synthelabo ordinary shares with respect to Sanofi-Synthelabo’s 2003 results; and

•  any other dividend that is paid after the settlement of the U.S. offer.

      You will receive the annual dividend declared with respect to Sanofi-Synthelabo’s 2003 results on the later to occur of (1) the date of the settlement of the offer (or the subsequent offering period, if any) and (2) the normal payment date for the dividend (expected to be at the beginning of June 2004). Your entitlement to receive these dividends, if any, in respect of the Sanofi-Synthelabo ordinary shares, including Sanofi-Synthelabo ordinary shares represented by Sanofi-Synthelabo ADSs, that you receive in the U.S. offer is in addition to the standard entitlement. Sanofi-Synthelabo reserves the right to pay an interim dividend with respect to Sanofi-Synthelabo’s 2003 results.

      16. Fractional Entitlements. You will not receive any fraction of a Sanofi-Synthelabo ADS. Instead, you will receive, after combining all fractional Sanofi-Synthelabo ADSs to which you would otherwise be entitled, cash in an amount equal to the product of that fraction and the average sale price per Sanofi-Synthelabo ADS, net of expenses, realized on the New York Stock Exchange in the sale by the U.S. ADS exchange agent of all the aggregated fractional Sanofi-Synthelabo ADSs that would have otherwise been issued in the offers. The sale of the aggregated Sanofi-Synthelabo ADSs on the New York Stock Exchange will occur no later than six trading days following the settlement of the offers. Payment of cash in lieu of any fractional Sanofi-Synthelabo ADS that

13

you would otherwise have been entitled to receive pursuant to the terms of the U.S. offer will be paid to you as promptly as practicable.

      17. Substitute Form W-9. Under United States federal income tax law, if you tender your Aventis ADSs, you generally are required to furnish the U.S. ADS exchange agent either (i) a properly completed Substitute Form W-9 (below) with your correct taxpayer identification number (“TIN”), if you are a U.S. person, or (ii) a properly completed appropriate Internal Revenue Service Form W-8, if you are not a U.S. person.

      Use Substitute Form W-9 only if you are a U.S. person, including a resident alien individual. You will be subject to United States federal backup withholding at a rate of 28% on all reportable payments made to you pursuant to the U.S. offer if (i) you do not furnish your TIN to the requester, (ii) you do not certify your TIN, (iii) the Internal Revenue Service tells the requester that you furnished an incorrect TIN, or (iv) you do not certify to the requester that you are not subject to backup withholding. Certain payees are exempt from backup withholding. See the instructions referred to below on whether you are an exempt payee.

      Backup withholding is not an additional tax. You may credit any amounts withheld by backup withholding against your regular United States federal income tax liability or, if backup withholding results in an overpayment of taxes, claim a refund from the Internal Revenue Service.

      If you have not been issued a TIN, you may write “Applied For” in the space provided in part I of the Substitute Form W-9 if you have applied for a TIN or intend to apply for a TIN. In that case, you must also complete the Certificate of Awaiting Taxpayer Identification Number attached to this ADS letter of transmittal. The U.S. ADS exchange agent will withhold 28% of all reportable payments unless you provide a TIN to the U.S. ADS exchange agent, or have otherwise established an exemption from backup withholding, by the time of payment.

      You are generally exempt from backup withholding if you are a nonresident alien or a foreign entity (including a disregarded domestic entity with a foreign owner) and give the requester the appropriate completed Form W-8. You will find further information in Internal Revenue Service Publication 515, “Withholding of Tax on Nonresident Aliens and Foreign Entities”. You can receive the applicable Form W-8 from the information agent.

      If you fail to furnish your correct TIN to the U.S. ADS exchange agent, you are subject to a penalty of $50 for each such failure unless your failure is due to reasonable cause and not to willful neglect. If you make a false statement with no reasonable basis that results in no backup withholding, you are subject to a $500 penalty. Willfully falsifying certifications or affirmations may subject you to criminal penalties, including fines and/or imprisonment.

      Important: This ADS letter of transmittal (or facsimile thereof), together with any required signature guarantees, or, in the case of a book-entry transfer, an “agent’s message”, and any other required documents, must be received by the U.S. ADS exchange agent prior to the expiration of the U.S. offer, and either ADRs evidencing the tendered Aventis ADSs must be received by the U.S. ADS exchange agent or Aventis ADSs must be delivered pursuant to the procedures for book-entry transfer, in each case prior to the expiration date of the U.S. offer, or the tendering Aventis ADS holder must comply with the procedures for guaranteed delivery.

14

IMPORTANT TAX INFORMATION

      Under the federal income tax law, a stockholder whose tendered Aventis ADSs are accepted for payment is generally required by law to provide the U.S. ADS exchange agent (as payer) with such stockholder’s correct TIN on Substitute Form W-9 below or otherwise establish a basis for exemption from backup withholding. If such stockholder is an individual, the TIN is such stockholder’s social security number. If the U.S. ADS exchange agent is not provided with the correct TIN, the stockholder may be subject to a $50 penalty imposed by the Internal Revenue Service and payments that are made to such stockholder with respect to Aventis ADSs purchased pursuant to the U.S. offer may be subject to backup withholding of 28%.

      Certain stockholders (including, among others, all corporations and certain foreign individuals) are not subject to these backup withholding and reporting requirements. In order for a foreign individual to qualify as an exempt recipient, such individual must submit an appropriate Form W-8, signed under penalties of perjury, attesting to such individual’s exempt status. An appropriate Form W-8 can be obtained from the U.S. ADS exchange agent. Exempt stockholders should furnish their TIN, check the “Exempt from backup withholding” box on the face of the Substitute Form W-9, and sign, date and return the Substitute Form W-9 to the U.S. ADS exchange agent. See the enclosed Guidelines for Certification of Taxpayer Identification Number on Substitute Form W-9 for additional instructions. A stockholder should consult his or her tax advisor as to such stockholder’s qualification for an exemption from backup withholding and the procedure for obtaining such exemption.

      If backup withholding applies, the U.S. ADS exchange agent is required to withhold 28% of any reportable payments made to the stockholder. Backup withholding is not an additional tax. Rather, the federal income tax liability of persons subject to backup withholding will be reduced by the amount of tax withheld. If withholding results in an overpayment of taxes, a refund may be obtained from the Internal Revenue Service.

Purpose of Substitute Form W-9

      To prevent backup withholding on payments that are made to a stockholder with respect to Aventis ADSs purchased pursuant to the U.S. offer, the stockholder is required to notify the U.S. ADS exchange agent of such stockholder’s correct TIN by completing the form below certifying that (a) the TIN provided on Substitute Form W-9 is correct (or that such stockholder is awaiting a TIN), (b) that (i) such stockholder is exempt from backup withholding, (ii) such stockholder has not been notified by the Internal Revenue Service that such stockholder is subject to backup withholding as a result of a failure to report all interest or dividends or (iii) the Internal Revenue Service has notified such stockholder that such stockholder is no longer subject to backup withholding and (c) that such stockholder is a U.S. person (including a U.S. resident alien).

What Number to Give the U.S. ADS Exchange Agent

      The stockholder is required to give the U.S. ADS exchange agent the social security number or employer identification number of the record holder of the Aventis ADSs tendered hereby. If the Aventis ADSs are in more than one name or are not in the name of the actual owner, consult the enclosed Guidelines for Certification of Taxpayer Identification Number on Substitute Form W-9 for additional guidance on which number to report. If the tendering stockholder has not been issued a TIN and has applied for a number or intends to apply for a number in the near future, the stockholder should write “Applied For” in the space provided for the TIN in Part I, and sign and date the Substitute Form W-9 and the Certificate of Awaiting Taxpayer Identification Number. If “Applied For” is written in Part I, the U.S. ADS exchange agent will withhold 28% of all reportable payments to such stockholder unless a TIN is provided to the U.S. ADS exchange agent by the time of payment.

15

TO BE COMPLETED BY ALL TENDERING ADS HOLDERS

(See Instruction 17)

PAYER’S NAME: THE BANK OF NEW YORK, AS U.S. ADS EXCHANGE AGENT

     THE SUBSTITUTE FORM W-9 BELOW MUST BE COMPLETED AND SIGNED. Please provide your social security number or other taxpayer identification number (“TIN”) and certify that you are not subject to backup withholding.

Substitute Form W-9 Department of the Treasury Internal Revenue Service Payer’s Request for TIN and Certification
Name:
Please check the appropriate box indicating your status: o  Individual/Sole proprietor   o Corporation    o Partnership   o Other	o Exempt from backup withholding
Address (number, street, and apt. or suite no.)
City, state, and ZIP code

Part I  TIN

PLEASE PROVIDE YOUR TIN ON THE APPROPRIATE LINE AT THE RIGHT. For most individuals, this is your social security number. If you do not have a number, see the enclosed Guidelines for Certification of Taxpayer Identification Number on Substitute Form W-9. If you are awaiting a TIN, write “Applied For” in this Part I, complete the “Certificate Of Awaiting Taxpayer Identification Number” below and see “IMPORTANT TAX INFORMATION”.

Social Security Number OR Employer Identification Number

Part II       Certification

Under penalties of perjury, I certify that:

(1) The number shown on this form is my correct Taxpayer Identification Number (or I am waiting for a number to be issued to me), and

(2) I am not subject to backup withholding because (a) I am exempt from backup withholding, or (b) I have not been notified by the IRS that I am subject to backup withholding as a result of a failure to report all interest or dividends, or (c) the IRS has notified me that I am no longer subject to backup withholding, and

(3) I am a U.S. person (including a U.S. resident alien).

Certification Instructions — You must cross out item (2) above if you have been notified by the IRS that you are currently subject to backup withholding because you have failed to report all interest and dividends on your tax return.

The IRS does not require your consent to any provision of this document other than the certifications required to avoid backup withholding.

Sign
Here Signature of
U.S. person 4 Date 4

NOTE: FAILURE TO COMPLETE AND RETURN THE SUBSTITUTE FORM W-9 MAY RESULT IN BACKUP WITHHOLDING OF 28% OF ANY PAYMENTS MADE TO YOU ON ACCOUNT OF THE OFFER. PLEASE REVIEW THE ENCLOSED GUIDELINES FOR CERTIFICATION OF TAXPAYER IDENTIFICATION NUMBER ON SUBSTITUTE FORM W-9 FOR ADDITIONAL DETAILS, AND PLEASE SEE “IMPORTANT TAX INFORMATION”.

COMPLETE THE FOLLOWING CERTIFICATION IF YOU WROTE “APPLIED FOR”

INSTEAD OF A TIN ON THE SUBSTITUTE FORM W-9.

CERTIFICATE OF AWAITING TAXPAYER IDENTIFICATION NUMBER

I certify under penalties of perjury that a taxpayer identification number has not been issued to me, and either (a) I have mailed or delivered an application to receive a TIN to the appropriate Internal Revenue Service Center or Social Security Administration Office or (b) I intend to mail or deliver an application in the near future. I understand that if I do not provide a TIN by the time of payment, 28% of all reportable payments made to me will be withheld.

Sign
Here Signature of
U.S. person 4 Date 4

     Questions and requests for assistance or additional copies of the prospectus, ADS letter of transmittal, the notice of guaranteed delivery and other tender offer materials may be directed to the information agent at the telephone number and location listed below. You may also contact your broker, dealer, commercial bank, trust company or other nominee for assistance concerning the U.S. offer:

The Information Agent for the U.S. Offer is:

105 Madison Avenue

New York, New York 10016

(212) 929-5500 (Call Collect)

or

Call Toll-Free (800) 322-2885

Email-proxy@mackenziepartners.com

The Joint Dealer-Managers for the U.S. Offer are:

Merrill Lynch & Co.

4 World Financial Center
New York, New York 10080
Toll-Free Call: (866) 276-1462 The Equitable Tower, 787 Seventh Avenue
New York, New York 10019
(212) 841-3700

EX-99.A.1.II

Exhibit (a)(1)(ii)

NOTICE OF GUARANTEED DELIVERY

For the Tender of American Depositary Shares

of

AVENTIS

(CUSIP: 053561106; ISIN: US0535611067)

Pursuant to the U.S. Offer to Exchange

by

SANOFI-SYNTHELABO

(Not to be used for Signature Guarantees)

THE U.S. OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 5:00 P.M., NEW YORK CITY TIME, ON MAY 28, 2004, UNLESS THE U.S. OFFER IS EXTENDED.

       This notice of guaranteed delivery, or a form substantially equivalent to this notice of guaranteed delivery, must be used for acceptance of the Offer described in the prospectus, dated April 9, 2004 (the “prospectus”), in respect of the American depositary shares (“ADSs”) of Aventis, a French société anonyme, if certificates evidencing Aventis ADSs are not immediately available or if the procedure for book-entry transfer cannot be completed on a timely basis, or if the time will not permit all required documents to reach the U.S. ADS exchange agent prior to the expiration of the U.S. offer. This notice of guaranteed delivery may be delivered by hand, transmitted by facsimile transmission or mailed to the U.S. ADS exchange agent and must include a guarantee by an Eligible Institution (as defined below) in the form set out in this notice of guaranteed delivery. If a message is transmitted through The Depository Trust Company pursuant to which the participant agrees to be bound by the terms set forth herein, an agent’s message must be delivered. See “The Offers — Procedures for Tendering Aventis ADSs — Guaranteed Delivery” in the prospectus.

The U.S. ADS Exchange Agent for the U.S. Offer is:

THE BANK OF NEW YORK

By Mail:

The Bank of New York
Aventis Exchange
P.O. Box 859208
Braintree, MA 02185-9208 By Hand:

The Bank of New York
Reorganization Services
101 Barclay Street
Receive and Deliver Window, Street Floor
New York, NY 10286 By Overnight Courier:

The Bank of New York
Aventis Exchange
161 Bay State Road
Braintree, MA 02184

Facsimile Transmission:

(Eligible Institutions Only)

(781) 380-3388

      DELIVERY OF THIS NOTICE OF GUARANTEED DELIVERY TO AN ADDRESS OTHER THAN AS SET FORTH ABOVE OR TRANSMISSION OF INSTRUCTIONS VIA FACSIMILE TRANSMISSION OTHER THAN AS SET FORTH ABOVE WILL NOT CONSTITUTE A VALID DELIVERY TO THE U.S. ADS EXCHANGE AGENT.

      THIS FORM IS NOT TO BE USED TO GUARANTEE SIGNATURES. IF A SIGNATURE ON AN ADS LETTER OF TRANSMITTAL IS REQUIRED TO BE GUARANTEED BY AN “ELIGIBLE INSTITUTION” UNDER THE INSTRUCTIONS TO THE ADS LETTER OF TRANSMITTAL, SUCH SIGNATURE GUARANTEE MUST APPEAR IN THE APPLICABLE SPACE PROVIDED IN THE SIGNATURE BOX IN THE ADS LETTER OF TRANSMITTAL.

      THE GUARANTEE ON THE REVERSE SIDE MUST BE COMPLETED.

Ladies and Gentlemen:

     The undersigned hereby tenders to Sanofi-Synthelabo, a French société anonyme, upon the terms and subject to the conditions set forth in the prospectus, dated April 9, 2004 (the “prospectus”), and the related ADS letter of transmittal (which, together with any amendments or supplements thereto, collectively constitute the “U.S. offer”), receipt of each of which is hereby acknowledged, the number of American depositary shares (“ADSs”) of Aventis specified below pursuant to the guaranteed delivery procedures described in the prospectus under “The Offers — Procedures for Tendering Aventis ADSs — Guaranteed Delivery”.

Names(s) of Record Holder(s)

Address(es)

Zip Code

(Area Code) Telephone No.

X 

X 

Signature(s) of Record Holder(s)

Number of Aventis ADSs

Certificate Nos. (if available)

Indicate account number at Book-Entry Transfer Facility if Aventis ADSs will be tendered by book-entry transfer:

Account Number

Dated: ________________________________________________________________________________, 2004

Dated: ________________________________________________________________________________, 2004

MIX AND MATCH ELECTION
(Complete only if you would like to exercise the mix and match election.)
1	Enter the number of Aventis ADSs for which you would like to make a mix and match election. Note: You must also complete Box 2A and/or Box 2B if you make this election. In addition, the number in Box 1 must be less than or equal to the total number of Aventis ADSs tendered.	1
2A	Enter the number of Aventis ADSs for which you would like to make the All Stock Election.	2A
2B	Enter the number of Aventis ADSs for which you would like to make the All Cash Election. Note: The sum of the number in Box 2A and the number in Box 2B must equal the number in Box 1.	2B

GUARANTEE

(NOT TO BE USED FOR SIGNATURE GUARANTEE)

     The undersigned, a bank, broker, dealer, credit union, savings association or other entity that is a member in good standing of the Securities Transfer Agents Medallion Program or any other “eligible guarantor institution,” as defined in Rule 17Ad-15 of the Securities Exchange Act of 1934, as amended (each an “Eligible Institution” and collectively, “Eligible Institutions”), hereby guarantees the delivery to the Depositary, at one of its addresses set forth above, of the ADSs tendered by this notice of guaranteed delivery in proper form for transfer, or confirmation of the book-entry transfer of Shares into the Depositary’s account at The Depository Trust Company, in either case together with delivery of a properly completed and duly executed ADS letter of transmittal (or a facsimile thereof) with any required signature guarantee, or an agent’s message (as defined in the prospectus), and any other documents required by the ADS letter of transmittal, within three New York Stock Exchange trading days after the date of execution of this notice of guaranteed delivery.

     The Eligible Institution that completes this form must communicate the guarantee to the Depositary and must deliver the ADS letter of transmittal and ADSs to the Depositary within the time period indicated herein. Failure to do so may result in financial loss to such Eligible Institution.

	X
Name of Firm	Authorized Signature
Address	Name (Please Print)
Zip Code	Title
	Dated:                                                                                                      , 2004
(Area Code) Telephone No.

NOTE: DO NOT SEND CERTIFICATES EVIDENCING AVENTIS ADSs WITH THIS NOTICE. SUCH CERTIFICATES SHOULD BE SENT WITH YOUR ADS LETTER OF TRANSMITTAL.

EX-99.A.1.III

Exhibit (a)(1)(iii)

Merrill Lynch & Co.

U.S. OFFER TO EXCHANGE

All Ordinary Shares, including

Ordinary Shares Represented by American Depositary Shares

of

AVENTIS

(CUSIP: 053561106; ISIN: US0535611067)

Pursuant to the Prospectus, dated April 9, 2004

by

SANOFI-SYNTHELABO

THE U.S. OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 5:00 P.M., NEW YORK CITY TIME, ON MAY 28, 2004, UNLESS THE U.S. OFFER IS EXTENDED.

April 12, 2004

To Brokers, Dealers, Commercial Banks, Trust Companies and Other Nominees:

      We have been appointed by Sanofi-Synthelabo, a French société anonyme, to act as joint dealer-managers in connection with Sanofi-Synthelabo’s offer to exchange: (a) each American depositary share (“ADS”) of Aventis, a French société anonyme, for 1.6667 Sanofi-Synthelabo ADSs (each Sanofi-Synthelabo ADS representing one-half of one Sanofi-Synthelabo ordinary share) and an amount in cash in U.S. dollars equal to €11.50, and (b) each Aventis ordinary share (other than Aventis ordinary shares represented by Aventis ADSs) for 0.8333 of a Sanofi-Synthelabo ordinary share and an amount in cash in U.S. dollars equal to €11.50, in each case upon the terms and subject to the conditions set forth in the prospectus, dated April 9, 2004 (the “prospectus”), and the related ADS letter of transmittal and form of acceptance (which, as amended or supplemented from time to time, constitute the “U.S. offer”) enclosed herewith. Terms used in this document to the extent not defined herein shall have the same meaning as in the prospectus.

      Please furnish copies of the enclosed materials to those of your clients for whose accounts you hold Aventis ADSs. Enclosed herewith for your information and forwarding to your clients are copies of the following documents:

1.	The prospectus, dated April 9, 2004.
2.	The ADS letter of transmittal to be used by holders of Aventis ADSs to accept the U.S. offer to tender Aventis ADSs. Holders may also use the ADS letter of transmittal to make a mix and match election in order to receive a greater proportion of the consideration in Sanofi-Synthelabo ADSs or in cash than the standard entitlement described above.
3.	The notice of guaranteed delivery to be used by holders of Aventis ADSs to accept the U.S. offer if certificates evidencing Aventis ADSs and all other required documents are not immediately available or cannot be delivered to the U.S. ADS exchange agent on or prior to the expiration date of the U.S. offer or if the procedure for book-entry transfer cannot be completed by the expiration date of the U.S. offer.
4.	A form of letter to be sent to your clients for whose accounts you hold Aventis ADSs, with space provided for obtaining such clients’ instructions with regard to the U.S. offer.
5.	Guidelines for Certification of Taxpayer Identification Number on Substitute Form W-9.

      THE U.S. OFFER MAY NOT BE ACCEPTED IN RESPECT OF AVENTIS ORDINARY SHARES BY MEANS OF AN ADS LETTER OF TRANSMITTAL AND NOTICE OF GUARANTEED DELIVERY. IF YOUR CLIENTS HOLD AVENTIS ORDINARY SHARES, THEY SHOULD USE THE FORMS OF ACCEPTANCE SENT BY THE FRENCH

INTERMEDIARIES FOR TENDERING SUCH SECURITIES INTO THE U.S. OFFER BY FOLLOWING THE INSTRUCTIONS SET FORTH ON SUCH FORMS. ADDITIONAL INFORMATION CAN BE OBTAINED FROM MACKENZIE PARTNERS, INC., THE INFORMATION AGENT FOR THE U.S. OFFER, AT (212) 929-5500.

      We urge you to contact your clients as promptly as possible.

      1. The U.S. offer is an offer by Sanofi-Synthelabo to exchange (a) each Aventis ADS for 1.6667 Sanofi-Synthelabo ADSs (each Sanofi-Synthelabo ADS representing one-half of one Sanofi-Synthelabo ordinary share) and an amount in cash in U.S. dollars equal to €11.50, and (b) each Aventis ordinary share (other than Aventis ordinary shares represented by Aventis ADSs) held by U.S. holders for 0.8333 of a Sanofi-Synthelabo ordinary share and an amount in cash in U.S. dollars equal to €11.50, in each case on the terms and subject to the conditions set forth in the prospectus.

      The U.S. offer contains a mix and match election feature, whereby holders of Aventis ordinary shares and holders of Aventis ADSs may elect to receive for each of their tendered Aventis ordinary shares or Aventis ADSs either (i) more shares of Sanofi-Synthelabo ordinary shares or Sanofi-Synthelabo ADSs, as applicable, or (ii) more cash, in each case in comparison to the standard entitlement described above. Specifically, holders may elect to receive, in lieu of the standard entitlement described above:

•  1.0294 Sanofi-Synthelabo ordinary shares in exchange for each Aventis ordinary share tendered; or 2.0588 Sanofi-Synthelabo ADSs in exchange for each Aventis ADS tendered; or

•  €60.43 in cash, without interest, in exchange for each ordinary share of Aventis tendered; or an amount in U.S. dollars equal to €60.43, in cash, without interest, in exchange for each Aventis ADS tendered.

      The mix and match elections, however, are subject to proration and allocation adjustments that will ensure that, in the aggregate, 81.0% of the Aventis ordinary shares (including Aventis ordinary shares underlying the Aventis ADSs) tendered in the U.S. offer and the concurrent French offer and German offer will be exchanged for Sanofi-Synthelabo ordinary shares (including Sanofi-Synthelabo ordinary shares underlying Sanofi-Synthelabo ADSs) and 19.0% will be exchanged for cash.

      Holders are not required to make any election or to make the same election for all of the Aventis ordinary shares or Aventis ADSs that they tender. Holders tendering Aventis ADSs who wish to make a mix and match election may do so by completing the mix and match election part of the ADS letter of transmittal and submitting the properly completed ADS letter of transmittal to the U.S. ADS exchange agent prior to the expiration of the U.S. offer. Tendering Aventis ADS holders who have not properly completed and submitted a mix and match election prior to that time will receive the standard entitlement. Aventis ADS holders who make a mix and match election will not be informed of the exact number of shares of Sanofi-Synthelabo ADSs or the amount of cash that they will receive until settlement of the consideration under the U.S. offer.

      2. The U.S. offer is being made for all outstanding Aventis ADSs and all Aventis ordinary shares held by U.S. holders (within the meaning of Rule 14d-1(d) under the Securities Exchange Act). Sanofi-Synthelabo will, upon the terms and subject to the conditions of the U.S. offer, exchange the Aventis ADSs and Aventis ordinary shares validly tendered and not withdrawn before the expiration date of the U.S. offer. The term “expiration date” means 5:00 p.m., New York City time, on May 28, 2004 or, if the U.S. offer is extended, the latest time and date at which the U.S. offer, as so extended by Sanofi-Synthelabo, will expire.

      3. The U.S. offer is being made separately from (i) the French offer, which is open to holders of Aventis ordinary shares who are located in France and to holders of Aventis ordinary shares who are located outside of France, Germany and the United States, if, pursuant to the local laws and regulations applicable to those holders, they are permitted to participate in the French offer, and (ii) the German offer, which is open to holders of Aventis ordinary shares who are located in Germany. The U.S. offer, the French offer and the German offer are being made on substantially similar terms, and completion of the offers is subject to the same conditions, which include, among others, that securities representing at least 50% of the total share capital and voting rights in Aventis, calculated on a fully diluted basis, plus one Aventis ordinary share on the closing date of the offers, shall have been validly tendered and not properly withdrawn prior to the expiration date (the “minimum share condition”).

      4. The U.S. offer and withdrawal rights will expire on the expiration date, which will be 5:00 p.m., New York City time, on May 28, 2004, unless: (a) the French Autorité des marchés financiers (“AMF”) sets a later expiration date for the tender period of the French offer, (b) the AMF has not at that time set an expiration date for the tender period of the French offer, (c) the AMF subsequently extends the tender period of the French offer, or (d) the offers lapse or are withdrawn prior to that time. Sanofi-Synthelabo intends that the U.S. offer, the French offer and the German offer will expire simultaneously. If the

initial expiration date of the French offer is later than May 28, 2004, or if the French offer period is extended, Sanofi-Synthelabo will issue a press release announcing a corresponding extension of the U.S. offer.

      5. Exchange of Aventis ADSs tendered and accepted for exchange pursuant to the U.S. offer will be made only after timely receipt by the U.S. ADS exchange agent of (a) certificates evidencing the tendered Aventis ADSs or a timely book-entry confirmation of a book-entry transfer of such Aventis ADSs into the U.S. ADS exchange agent’s account at the Book-Entry Transfer Facility pursuant to the procedures set forth in the prospectus under “The U.S. Offer — Procedures for Tendering Aventis ADSs — Aventis ADSs in Book-Entry Form”, (b) a properly completed and duly executed ADS letter of transmittal (or facsimile thereof with an original manual signature), with any required signature guarantees, or an agent’s message in connection with a book-entry transfer, as defined in the prospectus under “The U.S. Offer — Procedures for Tendering Aventis ADSs — Aventis ADSs in Book-Entry Form”, and (c) any other documents required by the ADS letter of transmittal.

      6. Sanofi-Synthelabo will be deemed to have accepted for exchange all validly tendered and not withdrawn Aventis ADSs on the expiration date subject only to the satisfaction of the minimum share condition and the other conditions described in the prospectus. The AMF is expected to publish the definitive results of the offers not later than nine French trading days following the expiration date of the offer period. However, upon determination that the minimum tender condition has been met, the AMF will publish provisional results prior to its publication of the definitive results. If the conditions are not satisfied, Sanofi-Synthelabo will promptly return all tendered Aventis securities without acquiring them.

      7. In the event that the offers are successful, Sanofi-Synthelabo ordinary shares or Sanofi-Synthelabo ADSs, as applicable, and cash will be delivered to the tendering holders of Aventis securities following the publication by the AMF of the final results of the offers for Aventis securities. If the offers are consummated, the final settlement date for the offers is currently expected to be within approximately 12 to 18 French trading days following the expiration date of the offers. Similarly, in the event of a subsequent offering period, if any, settlement is expected to occur within 12 to 18 French trading days following the expiration of that subsequent offer period. With respect to the tendered Aventis ADSs only, the cash consideration payable in the U.S. offer will be paid in U.S. dollars calculated by converting the applicable amount in euros into U.S. dollars using a current spot exchange rate, less expenses. If Sanofi-Synthelabo ADSs will be evidenced by ADRs, tendering holders may not receive these certificates until approximately two weeks after the settlement date. For further information, see “The U.S. Offer” in the prospectus.

      8. In order to take advantage of the U.S. offer, the appropriate ADS letter of transmittal (or facsimile thereof), properly completed and duly executed, with any required signature guarantees, or an agent’s message in connection with book-entry transfer of Aventis ADSs, and any other documents required by the ADS letter of transmittal must be sent to the U.S. ADS exchange agent at its address set forth in the prospectus prior to the expiration date, and either (a) the certificates for tendered Aventis ADSs must be received by the U.S. ADS exchange agent or such Aventis ADSs must be tendered pursuant to the procedures for book-entry transfer described in the prospectus and a book-entry confirmation must be received by the U.S. ADS exchange agent (including an agent’s message if the tendering holder has not delivered an ADS letter of transmittal) in each case prior to the expiration date, or (b) such holder must comply with the guaranteed delivery procedures.

      9. A holder who desires to tender Aventis ADSs and whose ADRs evidencing such Aventis ADSs are not immediately available, who cannot comply with the procedure for book-entry transfer on a timely basis, or for whom time will not permit all required documents to reach the U.S. ADS exchange agent prior to the expiration date, may tender such Aventis ADSs by following the procedures for guaranteed delivery set forth in the prospectus. See “The U.S. Offer — Procedures for Tendering Aventis ADSs — Guaranteed Delivery.”

      10. Sanofi-Synthelabo will pay the brokerage fees, if any, and related value added taxes incurred by holders of Aventis securities tendering into the U.S. offer, up to a limit of 0.3% of the value of each Aventis security tendered, and subject to a maximum amount of €45 per account, including all taxes. Holders of Aventis securities will not be reimbursed for any brokerage fees in any event that the U.S. offer is withdrawn or is not completed. Financial intermediaries will be paid a fee, net of tax, of €0.20 per Aventis ordinary share, with a maximum fee of €45 per account. This fee will not be paid in the event that the U.S. offer is withdrawn or is not completed and will not be paid in any event with respect to tendered Aventis securities owned by such financial intermediaries. Any demands for the foregoing fees must be made in writing and delivered to the Bank of New York so that such demand is received on or prior to the date that is five days following the expiration date. Such demands may be faxed to the Bank of New York at (781) 381-3388 or sent to the Bank of New York at one of the addresses listed on the front page of the ADS letter of transmittal.

      YOUR PROMPT ACTION IS REQUESTED. WE URGE YOU TO CONTACT YOUR CLIENTS AS PROMPTLY AS POSSIBLE. THE U.S. OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 5:00 P.M., NEW YORK CITY TIME, ON MAY 28, 2004, UNLESS THE EXPIRATION DATE OF THE FRENCH OFFER PERIOD IS SET AT A LATER DATE OR UNLESS THE U.S. OFFER IS EXTENDED.

      Any inquiries you have with respect to the U.S. offer should be addressed to either of the joint dealer managers or MacKenzie Partners, Inc., the information agent at their respective addresses and telephone numbers set forth on the back of this letter.

      Requests for additional copies of the enclosed materials may be directed to the information agent.

Very truly yours,

Merrill Lynch, Pierce, Fenner & Smith
Incorporated BNP Paribas Securities Corp.

      NOTHING CONTAINED HEREIN OR IN THE ENCLOSED DOCUMENTS SHALL RENDER YOU OR ANY OTHER PERSON THE AGENT OF SANOFI-SYNTHELABO, THE DEALER MANAGER, THE INFORMATION AGENT OR THE U.S. EXCHANGE AGENT, OR ANY AFFILIATE OF THE FOREGOING, OR AUTHORIZE YOU OR ANY OTHER PERSON TO GIVE ANY INFORMATION OR USE ANY DOCUMENT OR MAKE ANY REPRESENTATION ON BEHALF OF ANY OF THEM WITH RESPECT TO THE U.S. OFFER NOT CONTAINED IN THE PROSPECTUS OR THE ADS LETTER OF TRANSMITTAL. EX-99.A.1.IV 6 e93031exv99waw1wiv.htm LETTER TO CLIENTS

Exhibit (a)(1)(iv)

U.S. OFFER TO EXCHANGE

All Ordinary Shares, including

Ordinary Shares Represented by American Depositary Shares

of

AVENTIS

(CUSIP: 053561106; ISIN: US0535611067)

Pursuant to the prospectus, dated April 9, 2004

by

SANOFI-SYNTHELABO

THE U.S. OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 5:00 P.M., NEW YORK CITY TIME, ON MAY 28, 2004, UNLESS THE U.S. OFFER IS EXTENDED.

April 12, 2004

To Our Clients:

      Enclosed for your consideration are a prospectus, dated April 9, 2004 (the “prospectus”), the related ADS letter of transmittal and a notice of guaranteed delivery in connection with the offer by Sanofi-Synthelabo, a French société anonyme, to exchange (a) each American depositary share (“ADS”) of Aventis, a French société anonyme, for 1.6667 Sanofi-Synthelabo ADSs (each Sanofi-Synthelabo ADS representing one-half of one Sanofi-Synthelabo ordinary share) and an amount in cash in U.S. dollars equal to €11.50 and (b) each Aventis ordinary share (other than Aventis ordinary shares represented by Aventis ADSs) for 0.8333 of a Sanofi-Synthelabo ordinary share and an amount in cash in U.S. dollars equal to €11.50, in each case on the terms and subject to the conditions set forth in the prospectus, the related ADS letter of transmittal and notice of guaranteed delivery (which, as amended or supplemented from time to time, constitute the “U.S. offer”).

      Terms used in this document to the extent not defined herein shall have the same meaning as in the prospectus.

      We are (and our nominee is) the holder of record of Aventis ADSs held by us for your account. A tender of such Aventis ADSs can be made only by us and pursuant to your instructions. The ADS letter of transmittal is furnished to you for your information only and cannot be used to tender Aventis ADSs held by us for your account.

      We request instructions as to whether you wish to tender any of or all the Aventis ADSs held by us for your account, pursuant to the terms and conditions set forth in the prospectus.

      1.     The U.S. offer is to exchange (a) each Aventis ADS for 1.6667 Sanofi-Synthelabo ADSs (each Sanofi-Synthelabo ADS representing one-half of one Sanofi-Synthelabo ordinary share) and an amount in cash in U.S. dollars equal to €11.50 and (b) each Aventis ordinary share (other than Aventis ordinary shares represented by Aventis ADSs) for 0.8333 of a Sanofi-Synthelabo ordinary share and an amount in cash in U.S. dollars equal to €11.50, in each case on the terms and subject to the conditions set forth in the prospectus.

      The U.S. offer contains a mix and match election, whereby holders of Aventis ordinary shares and holders of Aventis ADSs may elect to receive for each of their tendered Aventis ordinary shares or Aventis ADSs, as applicable, either (a) all

Sanofi-Synthelabo ordinary shares or Sanofi-Synthelabo ADSs, as applicable, or (b) all cash. Specifically, the mix and match election permits holders to receive, in lieu of the standard entitlement described above:

•  1.0294 Sanofi-Synthelabo ordinary shares in exchange for each Aventis ordinary share tendered; or 2.0588 Sanofi-Synthelabo ADSs in exchange for each Aventis ADS tendered; or

•  €60.43 in cash, without interest, in exchange for each ordinary share of Aventis tendered; or an amount in U.S. dollars equal to €60.43, in cash, without interest, in exchange for each Aventis ADS tendered.

      The mix and match elections are subject to proration and allocation adjustments that will ensure that, in the aggregate, 81.0% of the Aventis ordinary shares (including Aventis ordinary shares underlying the Aventis ADSs) tendered in the U.S. offer and the concurrent French offer and German offer will be exchanged for Sanofi-Synthelabo ordinary shares (including Sanofi-Synthelabo ordinary shares underlying Sanofi-Synthelabo ADSs) and 19.0% will be purchased for cash.

      Holders are not required to make any election or to make the same election for all of the Aventis ordinary shares or Aventis ADSs that they tender. Tendering holders who wish to make a mix and match election may do so by submitting the mix and match election form to the U.S. ADS exchange agent prior to the expiration of the U.S. offer. Tendering holders who have not properly completed and submitted a mix and match election form prior to that time will receive the standard entitlement. Holders who make a mix and match election will not be informed of the exact number of Sanofi-Synthelabo ordinary shares or Sanofi-Synthelabo ADSs or the amount of cash they will receive until settlement of the consideration under the U.S. offer.

      2.     The U.S. offer is being made for all outstanding Aventis ordinary shares held by U.S. holders (within the meaning of Rule 14d-1(d) under the Securities Exchange Act) and all outstanding Aventis ADSs. Sanofi-Synthelabo will, upon the terms and subject to the conditions of the U.S. offer, exchange the Aventis ordinary shares and Aventis ADSs validly tendered and not withdrawn before the expiration date of the U.S. offer. The term “expiration date” means 5:00 p.m., New York City time, on May 28, 2004, or, if the U.S. offer is extended, the latest time and date at which the U.S. offer, as so extended by Sanofi-Synthelabo, will expire.

      3.     This U.S. offer is being made on substantially the same terms as an offer for all Aventis ordinary shares being made in France (the “French offer”) and in Germany (the “German offer”) to the extent permitted by law and regulations, and Sanofi-Synthelabo will not be required to complete this U.S. offer unless the French offer and the German offer are completed. Sanofi-Synthelabo’s obligation to accept Aventis ordinary shares and Aventis ADSs in this U.S. offer is also subject to several conditions, including the condition that securities representing at least 50% of the total share capital and voting rights in Aventis, calculated on a fully diluted basis, plus one Aventis ordinary share are validly tendered and not properly withdrawn in the U.S. offer, the French offer and the German offer, on a combined basis (the “minimum share condition”).

      4.     The U.S. offer and withdrawal rights will expire on the expiration date, which will be 5:00 p.m., New York City time, on May 28, 2004, unless: (a) the French Autorité des marchés financiers (“AMF”) sets a later expiration date for the tender period of the French offer, (b) the AMF has not at that time set an expiration date for the tender period of the French offer, (c) the AMF subsequently extends the tender period of the French offer, or (d) the offers lapse or are withdrawn prior to that time. Sanofi-Synthelabo intends that the U.S. offer, the French offer and the German offer will expire simultaneously. If the initial expiration date of the French offer is later than May 28, 2004, or if the French offer period is extended, Sanofi-Synthelabo will issue a press release announcing a corresponding extension of the U.S. offer.

      5.     Exchange of Aventis ADSs tendered and accepted for exchange pursuant to the U.S. offer will be made only after timely receipt by the U.S. ADS exchange agent of (a) certificates evidencing the tendered Aventis ADSs or a timely book-entry confirmation of a book-entry transfer of such Aventis ADSs into the U.S. ADS exchange agent’s account at the Depository Trust Company pursuant to the procedures set forth in the prospectus under “The U.S. Offer — Procedures for Tendering Aventis ADSs”, (b) a properly completed and duly executed ADS letter of transmittal (or facsimile thereof with an original manual signature), with any required signature guarantees, or an agent’s message in connection with a book-entry transfer (as defined in the prospectus under “The U.S. Offer — Procedures for Tendering Aventis ADSs — Aventis ADSs in Book-Entry Form”), and (c) any other documents required by the ADS letter of transmittal.

      6.     Sanofi-Synthelabo will be deemed to have accepted for exchange all validly tendered and not withdrawn Aventis ordinary shares and Aventis ADSs on the expiration date subject only to the satisfaction of the minimum share condition and

2

the other conditions described in the prospectus. The AMF is expected to publish the results of the offers not later than nine French trading days following the expiration date of the offer period. However, upon determination that the minimum tender condition has been met, the AMF will publish provisional results prior to its publication of the definitive results. If the conditions are not satisfied, Sanofi-Synthelabo will promptly return all tendered Aventis securities without acquiring them.

      7.     Sanofi-Synthelabo expects that the delivery of any cash for tendered Aventis ordinary shares or Aventis ADSs will occur approximately 12 to 18 French trading days after the expiration date. Under no circumstances will interest be paid on the exchange of Aventis ordinary shares or Aventis ADSs tendered, regardless of any delay in making the exchange or extension of the expiration date. The cash consideration paid to holders tendering Aventis ordinary shares or Aventis ADSs will be paid in U.S. dollars, converted at a then current spot exchange rate, and distributed, net of expenses, to such holders. For further information, see “The U.S. Offer” in the prospectus.

      8.     Aventis ADS holders who fail to complete and sign the Substitute Form W-9 may be subject to U.S. federal income tax backup withholding at a rate of 28%. See Instruction 12 of the ADS letter of transmittal.

      If you wish to have us tender any or all of the Aventis ADSs held by us for your account, please so instruct us by completing, executing, detaching and returning to us the instruction form set forth below. If you authorize tender of your Aventis ADSs, all such Aventis ADSs will be tendered unless otherwise indicated in such instruction form. Please forward your instructions to us as soon as possible to allow us ample time to tender Aventis ADSs on your behalf prior to the expiration of the U.S. offer.

      The U.S. offer is made solely by the prospectus and is being made to all U.S. holders of Aventis ordinary shares and all holders of Aventis ADSs. If Sanofi-Synthelabo becomes aware of any valid statute or law of any jurisdiction prohibiting the making of the U.S. offer or the acceptance of Aventis ADSs pursuant thereto, Sanofi-Synthelabo will make a good-faith effort to comply with such statute or law. If, after such good-faith effort, Sanofi-Synthelabo cannot comply with such statute or law, the U.S. offer will not be made to (nor will tenders be accepted from or on behalf of) the holders of Aventis ADSs in such jurisdiction. The U.S. offer is not being made to, nor will tenders be accepted from, or on behalf of, holders of Aventis ordinary shares and Aventis ADSs in any jurisdiction in which the making or acceptance of the U.S. offer would not be in compliance with the laws of such jurisdiction. In any jurisdiction where the securities or blue-sky laws require the U.S. offer to be made by a licensed broker or dealer, the U.S. offer will be deemed made on behalf of Sanofi-Synthelabo by the dealer manager for the U.S. offer, or one or more registered brokers or dealers that are licensed under the laws of such jurisdiction. An envelope in which to return your instructions to us is enclosed.

3

INSTRUCTIONS WITH RESPECT TO THE

U.S. OFFER TO EXCHANGE

All Ordinary Shares, including

Ordinary Shares Represented by American Depositary Shares

of

AVENTIS

Pursuant to the Prospectus, dated April 9, 2004

by

SANOFI-SYNTHELABO

      The undersigned acknowledge(s) receipt of your letter enclosing the prospectus, dated April 9, 2004 (the “prospectus”), and the related ADS letter of transmittal, pursuant to an offer by Sanofi-Synthelabo to acquire all the issued and outstanding Aventis ordinary shares and Aventis ADSs, upon the terms and subject to the conditions and the related ADS letter of transmittal.

      This will instruct you to tender the number of Aventis ADSs indicated below (or, if no number is indicated below, all Aventis ADSs) that are held by you for the account of the undersigned, on the terms and subject to the conditions set forth in the prospectus and in the related ADS letter of transmittal.

      The undersigned understands and acknowledges that all questions as to validity, form and eligibility of the surrender of any Aventis ADSs submitted on my behalf to the U.S. ADS exchange agent will be determined by Sanofi-Synthelabo (which may delegate power in whole or in part to the U.S. ADS exchange agent) and such determination shall be final and binding.

Number of Aventis ADSs to be Tendered*

Dated:           , 2004

Mix and Match Election: (Complete only if you would like to exercise the mix and match election)
	Enter the number of Aventis ADSs for which you would like to make a mix and match election	1
	Enter the number of Aventis ADSs for which you would like to receive 2.0588 Sanofi-Synthelabo ADSs per tendered Aventis ADS.	2A
	Enter the number of Aventis ADSs for which you would like to receive an amount in U.S dollars equal to €60.43 in cash, without interest, per tendered Aventis ADS.	2B
	Note: The sum of the number in Box 2A and the number in Box 2B must equal the number in Box 1.

SIGN HERE

Signature(s)

Please Print Name

Address

Area Code and Telephone Number

Tax Identification or Social Security Number(s)

*  Unless otherwise indicated, you are deemed to have instructed us to tender all Aventis ADSs held by us for your account.

PLEASE RETURN THIS FORM TO THE BROKERAGE FIRM OR OTHER NOMINEE MAINTAINING YOUR ACCOUNT. EX-99.A.1.V 7 e93031exv99waw1wv.htm GUIDELINES FOR CERTIFICATION OF TAXPAYER ID NUMBER

Exhibit (a)(1)(v)

GUIDELINES FOR CERTIFICATION OF TAXPAYER IDENTIFICATION

NUMBER ON SUBSTITUTE FORM W-9

      Guidelines for Determining the Proper Identification Number for the Payee (You) to Give the Payer — Social Security numbers have nine digits separated by two hyphens: i.e., 000-00-0000. Employer identification numbers have nine digits separated by only one hyphen: i.e., 00-0000000. The table below will help determine the number to give the payer. All “Section” references are to the Internal Revenue Code of 1986, as amended. “IRS” is the Internal Revenue Service.

For this type of account:		Give the name and social security number of —
1.	Individual	The individual
2.	Two or more individuals (joint account)	The actual owner of the account or, if combined funds, the first individual on the account(1)
3.	Custodian account of a minor (Uniform Gift to Minors Act)	The minor(2)
4.	a. The usual revocable savings trust (grantor is also trustee)	The grantor-trustee(1)
	b. So-called trust account that is not a legal or valid trust under state law	The actual owner(1)
5.	Sole proprietorship or single-owner LLC	The owner(3)

For this type of account:		Give the name and employer identification number of —
6.	Sole proprietorship or single-member LLC	The owner(3)
7.	A valid trust, estate, or pension trust	The legal entity(4)
8.	Corporate or LLC electing corporate status on Form 8832	The corporation
9.	Association, club, religious, charitable, educational, or other tax-exempt organization	The organization
10.	Partnership or multi-member LLC	The partnership
11.	A broker or registered nominee	The broker or nominee
12.	Account with the Department of Agriculture in the name of a public entity (such as a state or local government, school district, or prison) that receives agricultural program payments	The public entity

(1)	List first and circle the name of the person whose number you furnish. If only one person on a joint account has a social security number, that person’s number must be furnished.
(2)	Circle the minor’s name and furnish the minor’s social security number.
(3)	You must show your individual name, but you may also enter your business or “doing business as” name. You may use either your social security number or your employer identification number (if you have one).
(4)	List first and circle the name of the legal trust, estate, or pension trust. (Do not furnish the taxpayer identification number of the personal representative or trustee unless the legal entity itself is not designated in the account title.)

NOTE: If no name is circled when there is more than one name listed, the number will be considered to be that of the first name listed.

GUIDELINES FOR CERTIFICATION OF TAXPAYER IDENTIFICATION NUMBER

ON SUBSTITUTE FORM W-9

Page 2

Obtaining a Number

If you do not have a taxpayer identification number, apply for one immediately. To apply for a SSN, get Form SS-5, Application for a Social Security Card, from your local Social Security Administration office. Get Form W-7, Application for IRS Individual Taxpayer Identification Number, to apply for a TIN, or Form SS-4, Application for Employer Identification Number, to apply for an EIN. You can get Forms W-7 and SS-4 from the IRS by calling 1 (800) TAX-FORM, or from the IRS Web Site at www.irs.gov.

Payees Exempt From Backup Withholding

Payees specifically exempted from backup withholding include:

1.	An organization exempt from tax under Section 501(a), an individual retirement account (IRA), or a custodial account under Section 403(b)(7) if the account satisfies the requirements of Section 401(f)(2).
2.	The United States or any of its agencies or instrumentalities.
3.	A state, the District of Columbia, a possession of the United States, or any of their political subdivisions or instrumentalities.
4.	A foreign government or any of its political subdivisions, agencies or instrumentalities.
5.	An international organization or any of its agencies or instrumentalities.

Payees that may be exempt from backup withholding include:

   6. A corporation.

   7. A foreign central bank of issue.

8.	A dealer in securities or commodities required to register in the United States, the District of Columbia, or a possession of the United States.
9.	A futures commission merchant registered with the Commodity Futures Trading Commission.

10.	A real estate investment trust.
11.	An entity registered at all times during the tax year under the Investment Company Act of 1940.
12.	A common trust fund operated by a bank under Section 584(a).

  13. A financial institution.

14.	A middleman known in the investment community as a nominee or custodian.
15.	A trust exempt from tax under Section 664 or described in Section 4947.

The chart below shows types of payments that may be exempt from backup withholding. The chart applies to the exempt recipients listed above, 1 through 15.

	THEN the payment is
If the payment is for . . .	exempt for . . .
Interest and dividend payments	All exempt recipients except for 9
Broker transactions	Exempt recipients 1 through 13. Also, a person registered under the Investment Advisers Act of 1940 who regularly acts as a broker

Exempt payees should complete a substitute Form W-9 to avoid possible erroneous backup withholding. Furnish your taxpayer identification number, check the appropriate box for your status, check the “Exempt from backup withholding” box, sign and date the form and return it to the payer. Foreign payees who are not subject to backup withholding should complete an appropriate Form W-8 and return it to the payer.

Privacy Act Notice. Section 6109 requires you to provide your correct taxpayer identification number to payers who must file information returns with the IRS to report interest, dividends, and certain other income paid to you to the IRS. The IRS uses the numbers for identification purposes and to help verify the accuracy of your return and may also provide this information to various government agencies for tax enforcement or litigation purposes and to cities, states, and the District of Columbia to carry out their tax laws, and may also disclose this information to other countries under a tax treaty, or to Federal and state agencies to enforce Federal nontax criminal laws and to combat terrorism. Payers must be given the numbers whether or not recipients are required to file tax returns. Payers must generally withhold 28% of taxable interest, dividend, and certain other payments to a payee who does not furnish a taxpayer identification number to a payer. Certain penalties may also apply.

Penalties

(1)	Failure to Furnish Taxpayer Identification Number. If you fail to furnish your correct taxpayer identification number to a payer, you are subject to a penalty of $50 for each such failure unless your failure is due to reasonable cause and not to willful neglect.
(2)	Civil Penalty for False Information with Respect to Withholding. If you make a false statement with no reasonable basis that results in no backup withholding, you are subject to a $500 penalty.
(3)	Criminal Penalty for Falsifying Information. Willfully falsifying certifications or affirmations may subject you to criminal penalties including fines and/or imprisonment.

FOR ADDITIONAL INFORMATION CONTACT YOUR TAX
CONSULTANT OR THE INTERNAL REVENUE SERVICE. EX-99.A.1.VI 8 e93031exv99waw1wvi.htm FORM OF ACCEPTANCE

Exhibit (a)(1)(vi)

      THIS DOCUMENT IS IMPORTANT AND REQUIRES YOUR IMMEDIATE ATTENTION. If you are uncertain about the U.S. offer or about the action you should take, you are recommended to seek your own personal financial advice immediately from an appropriately authorized independent professional advisor.

      If you have sold or otherwise transferred any of your registered holdings of Aventis ordinary shares, please pass a copy of this document and the accompanying prospectus, dated April 9, 2004 (the “prospectus”), as soon as possible to the purchaser or transferee, or to the stockbroker, bank or other agent through whom the sale or transfer was effected, for delivery to the purchaser or transferee. However, the offer is not being made directly or indirectly in any jurisdiction where prohibited by applicable law and such documents should not be distributed, forwarded or transmitted into or from any jurisdiction where prohibited by applicable law by means whatsoever including without limitation mail, facsimile, transmission, telex or telephone.

FORM OF ACCEPTANCE

To Tender Ordinary Shares

of

AVENTIS

(ISIN: FR0000130460)

Pursuant to the U.S. Offer to Exchange

by

SANOFI-SYNTHELABO

THE U.S. OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 5:00 P.M., NEW YORK CITY TIME, ON MAY 28, 2004 UNLESS THE U.S. OFFER IS EXTENDED.

       THE INSTRUCTIONS ACCOMPANYING THIS FORM OF ACCEPTANCE SHOULD BE READ CAREFULLY BEFORE THIS FORM OF ACCEPTANCE IS COMPLETED.

      ACCEPTANCE OF THE U.S. OFFER IN RESPECT OF AVENTIS ADSs CANNOT BE MADE BY MEANS OF THIS FORM OF ACCEPTANCE.

DESCRIPTION OF AVENTIS ORDINARY SHARES TENDERED
	AVENTIS ORDINARY SHARE(S) TENDERED
Name(s) and Address(es) of Registered owner(s)	(ATTACH ADDITIONAL SIGNED LIST, IF NECESSARY)
		Total Number of	Number
		Aventis Ordinary	of Aventis
		Shares	Ordinary
	Certificate	Represented by	Shares
	Number(s)	Certificate(s)	Tendered*
		Total Shares
* Unless otherwise indicated, it will be assumed that all Aventis ordinary shares described above are being tendered.

      This form of acceptance is to be completed by holders of ordinary shares, nominal value €3.82 per share, of Aventis, a French société anonyme. Your bank or broker can assist you in completing this form of acceptance. The instructions included with this form of acceptance must be followed. Questions and requests for assistance or for additional copies of the prospectus and this form of acceptance may be directed to MacKenzie Partners, Inc., the information agent, at the address and telephone numbers indicated below.

      Delivery of this form of acceptance and any other required documents to the French Financial Intermediary or U.S. custodian (each a “Financial Intermediary”) by holders of Aventis ordinary shares will be deemed an acceptance of the U.S. offer by such holder with respect to such Aventis ordinary shares subject to the terms and conditions set out in the prospectus and this form of acceptance.

      If you hold Aventis ordinary shares in pure registered (nominatif pur) form, you cannot tender them unless you first request that they be converted to administered registered (nominatif administre) form. Aventis ordinary shares held in pure registered form (nominatif pur) are registered in the books of Aventis and are held in an account maintained by Société Générale, the shareholder services provider that Aventis has appointed. Aventis ordinary shares held in administered registered form (nominatif administré) are also registered in the books of Aventis but are held in an account maintained by an authorized financial intermediary (intermediaire financier habilité) of your own choice. Aventis ordinary shares held in bearer form (au porteur) are not registered in the books of the company and are held in an account maintained by an authorized financial intermediary of your own choice. If you wish to tender Aventis ordinary shares that you hold in pure registered form, you must arrange with your Financial Intermediary to open an account in which your Aventis ordinary shares will be held. This process may involve the execution of a “mandat d’administration”, in the case of a request to convert your Aventis ordinary shares into administered registered form, or the execution of a “convention de service et d’ouverture de compte” in the case of a request to convert your Aventis ordinary shares into bearer form, the content of both contracts being prescribed by the French Autorité des marchés financiers (the “AMF”). You should then send Société Générale, in its capacity as Aventis’s shareholder services provider, an instruction to convert your Aventis ordinary shares to administered registered form or bearer form, as applicable, and the identification of the account to which your Aventis ordinary shares should be transferred. (Your authorized Financial Intermediary will provide you with the appropriate instruction form). Société Générale will then take the necessary steps to deliver your Aventis ordinary shares to the account identified in the instruction, in the case of conversion to administered registered form (nominatif administré), or to instruct the central depositary system (Euroclear France) to proceed with the conversion of your Aventis ordinary shares to bearer form and to deliver them to the identified account. The conversion takes approximately one to five French business days, and you will be responsible for any related fees, commissions and expenses. You may contact Société Générale at + 33 2 51 85 67 89 for assistance in converting your shares.

      Aventis ordinary shares held of record by persons who are non-U.S. holders cannot be tendered pursuant to the U.S. offer and can only be tendered pursuant to the concurrent French offer. Information on the French offer may be obtained from the information agent.

2

NOTE: SIGNATURE(S) MUST BE PROVIDED BELOW.

PLEASE READ THE INSTRUCTIONS SET FORTH IN THIS FORM OF ACCEPTANCE CAREFULLY.

      Ladies and Gentlemen:

      The undersigned hereby tenders to Sanofi-Synthelabo, a French société anonyme, the above-described ordinary shares of Aventis, a French société anonyme, pursuant to the prospectus, dated April 9, 2004 (the “prospectus”). For each tendered Aventis ordinary share, the undersigned shall receive 0.8333 of a Sanofi-Synthelabo ordinary share and amount in cash equal to €11.50, without interest (the “standard entitlement”), upon the terms and subject to the conditions set forth in the prospectus, receipt of which is hereby acknowledged, and in this form of acceptance (which, together with the prospectus and any amendments or supplements hereto or thereto, constitute the “U.S. offer”). The U.S. offer is being made in connection with Sanofi-Synthelabo’s offer to acquire all of the outstanding Aventis ordinary shares, including Aventis ordinary shares represented by Aventis ADSs.

      The U.S. offer contains a mix and match election feature that allows the undersigned to elect to receive for each tendered Aventis ordinary share, in lieu of the standard entitlement:

•  1.0294 Sanofi-Synthelabo ordinary shares; or

•  an amount in cash equal to €60.43, without interest.

      The undersigned is not required to make any election (in which case the undersigned shall automatically receive the standard entitlement) or to make the same election for all of the Aventis ordinary shares that the undersigned tenders in the U.S. offer. The undersigned understands that the mix and match elections are subject to proration and allocation adjustments that will ensure that, in the aggregate (and subject to adjustment if Aventis pays any dividend or interim dividend before the settlement of the offers), 81.0% of the Aventis ordinary shares (including Aventis ordinary shares represented by Aventis ADSs) tendered in the U.S. offer and the concurrent French offer and German offer will be exchanged for Sanofi-Synthelabo ordinary shares (including Sanofi-Synthelabo ordinary shares represented by Sanofi-Synthelabo ADSs) and 19.0% will be purchased for cash. The undersigned acknowledges that, if it makes a mix and match election, it will not be informed of the exact number of Sanofi-Synthelabo ordinary shares or the amount of cash that it shall receive until settlement of the consideration under the U.S. offer. The undersigned also acknowledges that, if it does not properly complete and submit its mix and match election pursuant to this form of acceptance, or if there are any errors or mistakes in completing the “Mix and Match Election” box, including errors in the number of eligible elections that can be made with respect to the tendered Aventis ordinary shares, Sanofi-Synthelabo shall be able to determine, in its sole discretion, that any such tendered Aventis ordinary shares shall receive the standard entitlement.

      The undersigned acknowledges that, if Aventis pays any dividend or any interim dividend in respect of the Aventis ordinary shares, including Aventis ordinary shares represented by Aventis ADSs, before the settlement of the offers, the consideration offered in exchange for each Aventis ordinary share and each Aventis ADS tendered will be reduced by an amount equal to the net value of the dividend paid per Aventis ordinary share in the manner described in the prospectus under “The U.S. Offer — Consideration Offered after Payment of Aventis Dividends”. In respect of any Sanofi-Synthelabo ordinary shares that a holder receives in exchange for Aventis ordinary shares that the undersigned tenders in the offers, the undersigned shall be entitled to receive any annual dividend with respect to Sanofi-Synthelabo’s 2003 results that is declared on the Sanofi-Synthelabo ordinary shares and any other dividend that is paid after the settlement of this exchange offer.

      On the terms and subject to the conditions of the U.S. offer (including, if the U.S. offer is extended or amended, the terms and conditions of such extension or amendment), and subject to, and effective upon, acceptance for exchange of, and exchange for, the Aventis ordinary shares tendered herewith in accordance with the terms of the U.S. offer, the undersigned hereby sells, assigns and transfers to, or upon the order of, Sanofi-Synthelabo, all right, title and interest in and to all of the Aventis ordinary shares being tendered hereby and any and all dividends, distributions (including, without limitation, distributions of additional Aventis ordinary shares), rights or other securities issued or issuable in respect of such Aventis ordinary shares on or after the settlement date of the U.S. offer, and appoints Sanofi-Synthelabo the true and lawful agent and attorney-in-fact of the undersigned with respect to such Aventis ordinary shares (and any distributions) with full power of substitution (such power of attorney being deemed to be an irrevocable power coupled with an interest) to the fullest extent of such holder’s rights with respect to such Aventis ordinary shares (and any distributions) (a) to transfer ownership of such Aventis ordinary shares (and any distributions) on the account books maintained by Euroclear, together in either such case

3

with all accompanying evidences of transfer and authenticity, to or upon the order of Sanofi-Synthelabo, (b) to present such Aventis ordinary shares (and any distributions) for transfer on the books of Aventis and (c) to receive all benefits and otherwise exercise all rights of beneficial ownership of such Aventis ordinary shares (and any distributions), all in accordance with the terms and the conditions of the U.S. offer.

      The undersigned hereby instructs the Financial Intermediary to tender, or to cause to be tendered, the Aventis ordinary shares as part of the French centralizing procedures within five French trading days after the expiration of the offer period.

      The undersigned hereby irrevocably appoints the designees of Sanofi-Synthelabo, and each of them, the attorneys-in-fact and proxies, each with full power of substitution, to the full extent of such holder’s rights with respect to the Aventis ordinary shares tendered hereby which have been accepted for exchange by Sanofi-Synthelabo and with respect to any distributions. Subject to applicable law, the designees of Sanofi-Synthelabo will, with respect to the Aventis ordinary shares (and any associated distributions) for which the appointment is effective, be empowered to exercise all voting and any other rights of such stockholder, as they, in their sole discretion, may deem proper at any ordinary, extraordinary or adjourned meeting of Aventis’s shareholders, by written consent in lieu of any such meeting or otherwise. This proxy and power of attorney shall be irrevocable and coupled with an interest in the tendered Aventis ordinary shares. Such appointment is effective upon the acceptance by Sanofi-Synthelabo of the Aventis ordinary shares tendered. If the U.S. offer is successful, Sanofi-Synthelabo will be deemed to have accepted for exchange Aventis ordinary shares validly tendered and not withdrawn on the expiration date of the offers, as set forth in the final results of the offers published by the French Autorité des marchés financiers (the “AMF”). Upon the effectiveness of such appointment, without further action, all prior powers of attorney, proxies and consents given with respect to such Aventis ordinary shares (and any associated distributions) will be revoked, and no subsequent powers of attorney, proxies, consents or revocations may be given (and, if given, will not be deemed effective). Sanofi-Synthelabo reserves the right to require that, in order for Aventis ordinary shares to be deemed validly tendered, immediately upon Sanofi-Synthelabo’s exchange of such Aventis ordinary shares, subject to applicable law, Sanofi-Synthelabo must be able to exercise full voting rights with respect to such Aventis ordinary shares (and any associated distributions), including voting at any meeting of shareholders.

      The undersigned hereby represents and warrants that the undersigned has full power and authority to tender, sell, assign and transfer the Aventis ordinary shares (and any distributions) tendered hereby and, when the same are accepted for exchange by Sanofi-Synthelabo, Sanofi-Synthelabo will acquire good, marketable and unencumbered title thereto, free and clear of all liens, restrictions, charges and encumbrances, and the same will not be subject to any adverse claim. The undersigned will, upon request, execute and deliver any additional documents deemed by the Financial Intermediary or Sanofi-Synthelabo to be necessary or desirable to complete the sale, assignment and transfer of the Aventis ordinary shares (and any distributions) tendered hereby. In addition, the undersigned will promptly remit and transfer to the Financial Intermediary for the account of Sanofi-Synthelabo any and all distributions in respect of the Aventis ordinary shares tendered hereby, accompanied by appropriate documentation of transfer; and, pending such remittance or appropriate assurance thereof, Sanofi-Synthelabo shall be entitled to all rights and privileges as owner of any such distributions and may withhold the entire consideration offered or deduct from the consideration offered the amount or value thereof, as determined by Sanofi-Synthelabo in its sole discretion.

      The undersigned has been informed that an application will be submitted by Sanofi-Synthelabo to list its Sanofi-Synthelabo ordinary shares on the Premier Marché of the Euronext Paris, subject to the successful completion of the U.S. and the concurrent French offer and German offer.

      The undersigned understands that Sanofi-Synthelabo will not issue any fraction of a Sanofi-Synthelabo ordinary share. Instead, each tendering stockholder who would otherwise be entitled to a fraction of a Sanofi-Synthelabo ordinary share, after combining all fractional Sanofi-Synthelabo ordinary shares to which the stockholder would otherwise be entitled, will receive cash in an amount equal to the product of that fraction and the average sale price per Sanofi-Synthelabo ordinary share, net of expenses, realized on the Euronext Paris in the sale of all of the aggregated fractional Sanofi-Synthelabo ordinary shares that would have otherwise been issued in the offers. The sale of the aggregated Sanofi-Synthelabo ordinary shares on the Euronext Paris will occur no later than six trading days following the settlement of the offers. Payment of cash in lieu of any fractional Sanofi-Synthelabo ordinary shares that a holder would otherwise have been entitled to receive pursuant to the terms of the U.S. offer will be paid to such holder as promptly as practicable.

      The undersigned agrees that under no circumstances will interest be paid on the exchange of Sanofi-Synthelabo ordinary shares and cash for Aventis ordinary shares tendered, regardless of any delay in making the exchange or extension of the

4

expiration date for the U.S. offer. The undersigned also understands that, if the offers are withdrawn or lapse, the Aventis securities that holders tendered in the offers will be promptly returned to such holders, without interest or any other payment being due.

      All authority conferred or agreed to be conferred pursuant to this form of acceptance shall not be affected by, and shall survive, the death or incapacity of and any obligation of the undersigned hereunder shall be binding upon the heirs, personal representatives, successors and assigns of the undersigned. Except as stated in the prospectus, this tender is irrevocable.

      The undersigned understands that the valid tender of Aventis ordinary shares pursuant to the procedures described in the prospectus under “The U.S. Offer — Procedures for Tendering Aventis Ordinary Shares”, and the instructions hereto, will constitute a binding agreement between the undersigned and Sanofi-Synthelabo upon the terms and subject to the conditions of the U.S. offer. The undersigned recognizes that under certain circumstances set forth in the prospectus, Sanofi-Synthelabo may not be required to accept for exchange any of the Aventis ordinary shares tendered hereby.

      The undersigned hereby instructs the Financial Intermediary to issue the check and register the Sanofi-Synthelabo ordinary shares to which is entitled in the name(s) of the holder(s) shown above under “Description of Aventis Ordinary Shares Tendered.” The undersigned hereby instructs the Financial Intermediary to credit the account maintained at Euroclear with any Aventis ordinary shares which are not tendered or are not accepted for exchange. The undersigned recognizes that the Financial Intermediary will not transfer any Aventis ordinary shares which are not exchanged pursuant to the U.S. offer from the name of the registered holder thereof to any other person.

      For further information, see “The U.S. Offer” in the prospectus.

      SUBJECT TO THE TERMS OF THE PROSPECTUS, THIS FORM OF ACCEPTANCE SHALL NOT BE CONSIDERED COMPLETE AND VALID, AND DELIVERY OF AVENTIS ORDINARY SHARES PURSUANT TO THE OFFER SHALL NOT BE MADE, UNTIL THE AVENTIS COMMON SHARES IN RESPECT OF WHICH THE OFFER IS BEING ACCEPTED AND ALL OTHER REQUIRED DOCUMENTATION HAVE BEEN RECEIVED BY THE FINANCIAL INTERMEDIARY. SANOFI-SYNTHELABO WILL DETERMINE IN ITS SOLE DISCRETION ALL QUESTIONS AS TO THE FORM OF DOCUMENTS, INCLUDING ANY NOTICE OF WITHDRAWAL AND THE VALIDITY, ELIGIBILITY (INCLUDING TIME OF RECEIPT) AND ACCEPTANCE OF TENDERED AVENTIS ORDINARY SHARES. SANOFI-SYNTHELABO’S DETERMINATION WILL BE FINAL AND BINDING ON ALL PARTIES.

5

MIX AND MATCH ELECTION
Complete only if you would like to exercise the mix and match election.
(See Instruction 10)
1	Enter the number of Aventis ordinary shares for which you would like to make a mix and match election.	1
	Note: You must also complete Box 2A and/or Box 2B if you make this election. In addition, the number in Box 1 must be less than or equal to the total number of Aventis ordinary shares tendered.
2A	Enter the number of Aventis ordinary shares for which you would like to make the All Stock Election.	2A
2B	Enter the number of Aventis ordinary shares for which you would like to make the All Cash Election.	2B
	Note: The sum of the number in Box 2A and the number in Box 2B must equal the number in Box 1.

SIGN HERE

(AND PLEASE COMPLETE SUBSTITUTE FORM W-9)

Signature(s) of Holder(s)

Dated: ______________________________ , 2004

          (Must be signed by registered owner(s) exactly as name(s) appear(s) on the certificates representing the Aventis ordinary shares or on a security position listing or by person(s) authorized to become registered owner(s) by endorsements, stock powers and documents transmitted herewith. If a signature is by an officer on behalf of a corporation or by an executor, administrator, trustee, guardian, attorney-in-fact, agent or other person acting in a fiduciary or representative capacity, please provide the following information.)

Name(s):

(Please Print)

Name of Firm:

Capacity (full title):

Address:

(Include Zip Code)

(Area Code) Telephone Number:

Taxpayer Identification or

Social Security No.:

(See Substitute Form W-9)

6

INSTRUCTIONS

FORMING PART OF THE TERMS AND CONDITIONS OF THE U.S. OFFER

      1.     Delivery of Form of Acceptance and Ordinary Shares. This form of acceptance is to be completed by shareholders if they are tendering Aventis ordinary shares to a French Financial Intermediary or U.S. custodian. A manually executed copy of this document may be used in lieu of the original. This form of acceptance properly completed and duly executed, and any other documents required by this form of acceptance, must be received by the Financial Intermediary at one of its addresses set forth herein on or prior to the expiration date. If Aventis ordinary shares are forwarded to the Financial Intermediary in multiple transfers, a properly completed and duly executed form of acceptance must accompany each such transfer.

      The method of delivery of this form of acceptance and all other required documents is at the election and risk of the tendering holder of Aventis ordinary shares. The delivery will be deemed made only when actually received by the Financial Intermediary. If such delivery is by mail, it is recommended that such documents be sent by registered mail, properly insured, with return receipt requested. In all cases, sufficient time should be allowed to assure timely delivery.

      No alternative, conditional or contingent tenders will be accepted and no fractional Aventis ordinary shares will be accepted for exchange. All tendering holders of Aventis ordinary shares by execution of this form of acceptance (or facsimile thereof) waive any right to receive any notice of the acceptance of their Aventis ordinary shares for exchange.

      2.     Inadequate Space. If the space provided herein is inadequate, the number of Aventis ordinary shares should be listed on a separate schedule attached hereto.

      3.     Signatures on Form of Acceptance; Stock Powers and Endorsements. If this form of acceptance is signed by the registered owners of the Aventis ordinary shares tendered hereby, the signature must correspond to the names as written on the face of the certificates without alteration, enlargement or any other change whatsoever.

      If any of the Aventis ordinary shares tendered hereby are owned of record by two or more joint owners, all such owners must sign this form of acceptance.

      If any of the tendered Aventis ordinary shares are registered in different names on several certificates, it will be necessary to complete, sign and submit as many separate forms of acceptance as there are different registrations of certificates.

      If this form of acceptance or any certificates or stock powers are signed by trustees, executors, administrators, guardians, attorneys-in-fact, officers of corporations or others acting in a fiduciary or representative capacity, such persons should so indicate when signing, and proper evidence satisfactory to Sanofi-Synthelabo of their authority so to act must be submitted.

      If this form of acceptance is signed by the registered owner(s) of the Aventis ordinary shares listed and transmitted hereby, no endorsements of certificates or separate stock powers are required unless payment is to be made to, or certificates for Aventis ordinary shares not tendered or accepted for payment are to be issued in the name of, a person other than the registered owner(s). Signatures on such certificates or stock powers must be guaranteed by an eligible institution.

      If this form of acceptance is signed by a person other than the registered owner of the certificate(s) listed, the certificate(s) must be endorsed or accompanied by the appropriate stock powers, in either case signed exactly as the name or names of the registered owner or holders appears on the certificate(s). Signatures on such certificates or stock powers must be guaranteed by an eligible institution.

      4.     Transfer Taxes. Sanofi-Synthelabo will pay or cause to be paid any transfer taxes with respect to the exchange of Aventis ordinary shares not based on income. If, however, a transfer tax is imposed based on income or for any reason other than the exchange of securities in this U.S. offer, then those transfer taxes, whether imposed on the registered holder or any other persons, will not be payable to the tendering holder.

7

      Except as provided in this Instruction 4, it will not be necessary for transfer tax stamps to be affixed to the Aventis ordinary shares certificates listed in this form of acceptance.

      5.     Requests for Assistance or Additional Copies. Questions and requests for assistance or for additional copies of the prospectus and the form of acceptance may be directed to the information agent or the dealer managers at their respective telephone numbers and locations set forth below. You may also contact your Financial Intermediary for assistance concerning the U.S. offer.

      6.     Conditions. This U.S. offer is being made on substantially the same terms as an offer for all Aventis ordinary shares being made in France (the “French offer”) and in Germany (the “German offer”) (to the extent permitted by law and regulations), and Sanofi-Synthelabo will not be required to complete this U.S. offer unless the French offer and German offer are completed. Sanofi-Synthelabo’s obligation to accept Aventis ordinary shares and Aventis ADSs in this U.S. offer is also subject to, among other things, the condition that securities representing at least 50% of the total share capital and voting rights in Aventis, calculated on a fully diluted basis, plus one Aventis ordinary share on the closing date of the offers, shall have been validly tendered and not properly withdrawn prior to the expiration date (the “minimum share condition”).

      7.     Holders of Aventis ADSs. Holders of record of Aventis ADSs, wherever resident, must use the ADS letter of transmittal in order to tender their Aventis ADSs into the U.S. offer. Holders of Aventis ADSs evidenced by ADRs have been sent an ADS letter of transmittal with the U.S. offer to exchange and may not tender Aventis ADSs using this form of acceptance. If any holder(s) of Aventis ADSs needs to obtain a copy of the ADS letter of transmittal, such holder(s) should contact the information agent at the address and telephone numbers set forth at the end of this form of acceptance.

      8.     No Interest. Under no circumstances will interest be paid on the exchange of Sanofi-Synthelabo ordinary shares and cash, for Aventis ordinary shares tendered, regardless of any delay in making the exchange or extension of the expiration date for the U.S. offer. For further information, see “The U.S. Offer” in the prospectus.

      9.     Expiration Date. The expiration date will be 5:00 p.m., New York City time, on May 28, 2004, unless: (a) the AMF sets a later expiration date for the tender period of the French offer, (b) the AMF has not at that time set an expiration date for the tender period of the French offer, (c) the AMF subsequently extends the tender period of the French offer, or (d) the offers lapse or are withdrawn prior to that time. Sanofi-Synthelabo intends that the U.S. offer, the French offer and the German offer will expire simultaneously. If the initial expiration date of the French offer is later than May 28, 2004, of if the French offer period is extended, Sanofi-Synthelabo will issue a press release announcing a corresponding extension of the U.S. offer.

      10.     Mix and Match Election. For each of your tendered Aventis ordinary shares, you may elect to receive either all Sanofi-Synthelabo ordinary shares or all cash, instead of the standard entitlement per Aventis ordinary share of 0.8333 of a Sanofi-Synthelabo ordinary share and an amount in cash equal to €11.50, without interest. Specifically, the mix and match election feature allows you to elect to receive for each of your tendered Aventis ordinary shares, in lieu of the standard entitlement described above:

• 1.0294 Sanofi-Synthelabo ordinary shares (the “All Stock Election”); or

• €60.43 in cash, without interest (the “All Cash Election”).

      You are not required to make any election (in which case you will automatically receive the standard entitlement) or make the same election for all of the Aventis ordinary shares that you tender. The mix and match elections, however, are subject to proration and allocation adjustments that will ensure that, in the aggregate, 81.0% of the Aventis ordinary shares (including Aventis ordinary shares underlying the Aventis ADSs) tendered in the U.S. offer and the concurrent French offer and German offer will be exchanged for Sanofi-Synthelabo ordinary shares (including Sanofi-Synthelabo ordinary shares underlying Sanofi-Synthelabo ADSs) and 19.0% will be purchased for cash. For additional information regarding the proration and allocation adjustments, see the prospectus under “The U.S. Offer — Mix and Match Election”.

      To make an All Stock Election or an All Cash Election with respect to any of your tendered Aventis ADSs, you must provide the information requested above in the box entitled “Mix and Match Election”. If there are any

8

errors or mistakes in completing the “Mix and Match Election” box, including errors in the number of eligible elections that can be made with respect to the tendered Aventis ordinary shares, Sanofi-Synthelabo shall be able to determine, in its sole discretion, that any such tendered Aventis ordinary shares shall receive the standard entitlement.

      11.     Consideration Offered after Payment of Dividends. If Aventis pays any dividend or any interim dividend in respect of the Aventis ordinary shares, including Aventis ordinary shares represented by Aventis ADSs, before the settlement of the offers, the consideration offered in exchange for each Aventis ordinary share tendered will be reduced by an amount equal to the net value of the dividend paid per Aventis ordinary share in the manner described under “The U.S. Offer — Consideration Offered after Payment of Aventis Dividends”.

      In respect of Sanofi-Synthelabo ordinary shares issued in exchange or part exchange for your tendered Aventis securities, you will be entitled to receive:

• any annual dividend that is approved to be paid on the Sanofi-Synthelabo ordinary shares with respect to Sanofi-Synthelabo’s 2003 results; and

• any other dividend that is paid after the settlement of the U.S. offer.

      You will receive the annual dividend declared with respect to Sanofi-Synthelabo’s 2003 results on the later to occur of (1) the date of the settlement of the offer (or the subsequent offering period, if any) and (2) the normal payment date for the dividend (expected to be at the beginning of June 2004). Your entitlement to receive these dividends, if any, in respect of the Sanofi-Synthelabo ordinary shares that you receive in the U.S. offer is in addition to the standard entitlement. Sanofi-Synthelabo reserves the right to pay an interim dividend with respect to Sanofi-Synthelabo’s 2003 results.

      12.     Fractional Entitlements. You will not receive any fraction of a Sanofi-Synthelabo ordinary share. Instead, you will receive, after combining all fractional Sanofi-Synthelabo ordinary shares to which you would otherwise be entitled, cash in an amount equal to the product of that fraction and the average sale price per Sanofi-Synthelabo ordinary share, net of expenses, realized on the Euronext Paris in the sale of all of the aggregated fractional Sanofi-Synthelabo ordinary shares that would have otherwise been issued in the offers. The sale of the aggregated Sanofi-Synthelabo ordinary shares on the Euronext Paris will occur no later than six trading days following the settlement of the offers. Payment of cash in lieu of any fractional Sanofi-Synthelabo ordinary shares that you would otherwise have been entitled to receive pursuant to the terms of the U.S. offer will be paid to you as promptly as practicable.

      13.     Substitute Form W-9. This section applies to you only if your Financial Intermediary has attached a Substitute Form W-9. Under United States federal income tax law, if you tender your Aventis ordinary shares, you generally are required to furnish the Financial Intermediary either (i) a properly completed Substitute Form W-9 (below) with your correct taxpayer identification number (“TIN”), if you are a United States person, or (ii) a properly completed appropriate Internal Revenue Service Form W-8, if you are a non-U.S. person.

      Use Substitute Form W-9 only if you are a U.S. person, including a resident alien individual. You will be subject to United States federal backup withholding at a rate of 28% on all reportable payments made to you pursuant to the U.S. offer if (i) you do not furnish your TIN to the requester, (ii) you do not certify your TIN, (iii) the Internal Revenue Service tells the requester that you furnished an incorrect TIN, or (iv) you do not certify to the requester that you are not subject to backup withholding. Certain payees are exempt from backup withholding. See the instructions referred to below on whether you are an exempt payee.

      Backup withholding is not an additional tax. You may credit any amounts withheld by backup withholding against your regular United States federal income tax liability or, if backup withholding results in an overpayment of taxes, claim a refund from the Internal Revenue Service.

      If you have not been issued a TIN, you may write “Applied For” in the space provided in part I of the Substitute Form W-9 if you have applied for a TIN or intend to apply for a TIN. In that case, you must also complete the Certificate of Awaiting Taxpayer Identification Number attached to this form of acceptance. The Financial Intermediary will withhold 28% of all reportable payments unless you provide a TIN to the Financial Intermediary, or have otherwise established an exemption from backup withholding by the time of payment.

9

      You are generally exempt from backup withholding if you are a nonresident alien or a foreign entity (including a disregarded domestic entity with a foreign owner) and give the requester the appropriate completed Form W-8. You will find further information in Internal Revenue Service Publication 515, “Withholding of Tax on Nonresident Aliens and Foreign Entities.” You can receive the applicable Form W-8 from the information agent.

      If you fail to furnish your correct TIN to the Financial Intermediary, you are subject to a penalty of $50 for each such failure unless your failure is due to reasonable cause and not to willful neglect. If you make a false statement with no reasonable basis that results in no backup withholding, you are subject to a $500 penalty. Willfully falsifying certifications or affirmations may subject you to criminal penalties, including fines and/or imprisonment.

      Important: this form of acceptance or a manually signed facsimile thereof (together with confirmation of book entry transfer and all other required documents) must be received by the Financial Intermediary on or prior to the expiration date.

10

IMPORTANT TAX INFORMATION

      Under the federal income tax law, a stockholder whose tendered Aventis ordinary shares are accepted for payment is generally required by law to provide the Financial Intermediary (as payer) with such stockholder’s correct TIN on Substitute Form W-9 below or otherwise establish a basis for exemption from backup withholding. If such stockholder is an individual, the TIN is such stockholder’s social security number. If the Financial Intermediary is not provided with the correct TIN, the stockholder may be subject to a $50 penalty imposed by the Internal Revenue Service and payments that are made to such stockholder with respect to Aventis ordinary shares purchased pursuant to the U.S. offer may be subject to backup withholding of 28%.

      Certain stockholders (including, among others, all corporations and certain foreign individuals) are not subject to these backup withholding and reporting requirements. In order for a foreign individual to qualify as an exempt recipient, such individual must submit an appropriate Form W-8, signed under penalties of perjury, attesting to such individual’s exempt status. An appropriate Form W-8 can be obtained from your Financial Intermediary. Exempt stockholders should furnish their TIN, check the “Exempt from backup withholdings” box on the face of the Substitute Form W-9, and sign, date and return the Substitute Form W-9 to your Financial Intermediary. See the enclosed Guidelines for Certification of Taxpayer Identification Number on Substitute Form W-9 for additional instructions. A stockholder should consult his or her tax advisor as to such stockholder’s qualification for an exemption from backup withholding and the procedure for obtaining such exemption.

      If backup withholding applies, the Financial Intermediary is required to withhold 28% of any reportable payments made to the stockholder. Backup withholding is not an additional tax. Rather, the federal income tax liability of persons subject to backup withholding will be reduced by the amount of tax withheld. If withholding results in an overpayment of taxes, a refund may be obtained from the Internal Revenue Service.

Purpose of Substitute Form W-9

      To prevent backup withholding on payments that are made to a stockholder with respect to Aventis ordinary shares purchased pursuant to the U.S. offer, the stockholder is required to notify the Financial Intermediary of such stockholder’s correct TIN by completing the form below certifying that (a) the TIN provided on Substitute Form W-9 is correct (or that such stockholder is awaiting a TIN), (b) that (i) such stockholder is exempt from backup withholding (ii) such stockholder has not been notified by the Internal Revenue Service that such stockholder is subject to backup withholding as a result of a failure to report all interest or dividends or (iii) the Internal Revenue Service has notified such stockholder that such stockholder is no longer subject to backup withholding and (c) that such stockholder is a U.S. person (including a U.S. resident alien).

What Number to Give the Financial Intermediary

      The stockholder is required to give the Financial Intermediary the social security number or employer identification number of the record holder of the Aventis ordinary shares tendered hereby. If the Aventis ordinary shares are in more than one name or are not in the name of the actual owner, consult the enclosed Guidelines for Certification of Taxpayer Identification Number on Substitute Form W-9 for additional guidance on which number to report. If the tendering stockholder has not been issued a TIN and has applied for a number or intends to apply for a number in the near future, the stockholder should write “Applied For” in the space provided for the TIN in Part I, and sign and date the Substitute Form W-9 and the Certificate of Awaiting Taxpayer Identification Number. If “Applied For” is written in Part I, the Financial Intermediary will withhold 28% of all reportable payments to such stockholder unless a TIN is provided to the Financial Intermediary by the time of payment.

11

TO BE COMPLETED BY ALL TENDERING HOLDERS

(See Instruction 13)

PAYER’S NAME:

     THE SUBSTITUTE FORM W-9 BELOW MUST BE COMPLETED AND SIGNED. Please provide your social security number or other taxpayer identification number (“TIN”) and certify that you are not subject to backup withholding.

Substitute Form W-9 Department of the Treasury Internal Revenue Service Payer’s Request for TIN and Certification
Name:
Please check the appropriate box indicating your status: o  Individual/Sole proprietor   o Corporation   o Partnership   o Other	o Exempt from backup withholding
Address (number, street, and apt. or suite no.)
City, state, and ZIP code

Part I  TIN

PLEASE PROVIDE YOUR TIN ON THE APPROPRIATE LINE AT THE RIGHT. For most individuals, this is your social security number. If you do not have a number, see the enclosed Guidelines for Certification of Taxpayer Identification Number on Substitute Form W-9. If you are awaiting a TIN, write “Applied For” in this Part I, complete the “Certificate Of Awaiting Taxpayer Identification Number” below and see “IMPORTANT TAX INFORMATION”.

Social Security Number OR Employer Identification Number

Part II       Certification

Under penalties of perjury, I certify that:

(1) The number shown on this form is my correct Taxpayer Identification Number (or I am waiting for a number to be issued to me), and

(2) I am not subject to backup withholding because (a) I am exempt from backup withholding, or (b) I have not been notified by the IRS that I am subject to backup withholding as a result of a failure to report all interest or dividends, or (c) the IRS has notified me that I am no longer subject to backup withholding, and

(3) I am a U.S. person (including a U.S. resident alien).

Certification Instructions — You must cross out item (2) above if you have been notified by the IRS that you are currently subject to backup withholding because you have failed to report all interest and dividends on your tax return.

The IRS does not require your consent to any provision of this document other than the certifications required to avoid backup withholding.

Sign
Here Signature of
U.S. person 4 Date 4

NOTE: FAILURE TO COMPLETE AND RETURN THE SUBSTITUTE FORM W-9 MAY RESULT IN BACKUP WITHHOLDING OF 28% OF ANY PAYMENTS MADE TO YOU ON ACCOUNT OF THE OFFER. PLEASE REVIEW THE ENCLOSED GUIDELINES FOR CERTIFICATION OF TAXPAYER IDENTIFICATION NUMBER ON SUBSTITUTE FORM W-9 FOR ADDITIONAL DETAILS, AND PLEASE SEE “IMPORTANT TAX INFORMATION”.

COMPLETE THE FOLLOWING CERTIFICATION IF YOU WROTE “APPLIED FOR”

INSTEAD OF A TIN ON THE SUBSTITUTE FORM W-9.

CERTIFICATE OF AWAITING TAXPAYER IDENTIFICATION NUMBER

I certify under penalties of perjury that a taxpayer identification number has not been issued to me, and either (a) I have mailed or delivered an application to receive a TIN to the appropriate Internal Revenue Service Center or Social Security Administration Office or (b) I intend to mail or deliver an application in the near future. I understand that if I do not provide a TIN by the time of payment, 28% of all reportable payments made to me will be withheld.

Sign
Here Signature of
U.S. person 4 Date 4

     Questions and requests for assistance or additional copies of the prospectus, this form of acceptance, the ADS letter of transmittal, the notice of guaranteed delivery and other tender offer materials may be directed to the information agent at the telephone number and location listed below. You may also contact your broker, dealer, commercial bank, trust company or other nominee for assistance concerning the U.S. offer:

The Information Agent for the U.S. Offer is:

105 Madison Avenue

New York, New York 10016

(212) 929-5500 (Call Collect)

or

Call Toll-Free (800) 322-2885

Email: proxy@mackenziepartners.com

The Joint Dealer-Managers for the U.S. Offer are:

Merrill Lynch & Co.
4 World Financial Center	The Equitable Tower, 787 Seventh Avenue
New York, New York 10080	New York, New York 10019
Toll-Free Call: (866) 276-1462	(212) 841-3700

EX-99.A.1.IV

LETTER TO CLIENTS

EX-99.A.1.V

GUIDELINES FOR CERTIFICATION OF TAXPAYER ID NUMBER

EX-99.A.1.VI

FORM OF ACCEPTANCE

EX-99.A.1.VII

Exhibit (a)(1)(vii)

April 12, 2004

MERRILL LYNCH & CO.

BNP PARIBAS

TRANSMITTED BY EUROCLEAR FRANCE S.A.

SANOFI-SYNTHELABO

OFFER TO EXCHANGE AVENTIS ORDINARY SHARES

(INCLUDING AVENTIS ORDINARY SHARES REPRESENTED BY AMERICAN DEPOSITARY SHARES)

HELD BY U.S. HOLDERS OF AVENTIS

II. TECHNICAL NOTICE TO INTERMEDIARIES WITH RESPECT TO THE U.S. OFFER

II. TECHNICAL NOTICE TO INTERMEDIARIES WITH RESPECT TO THE U.S. OFFER

SANOFI-SYNTHELABO

OFFER TO EXCHANGE AVENTIS ORDINARY SHARES (INCLUDING AVENTIS ORDINARY SHARES REPRESENTED BY AMERICAN DEPOSITARY SHARES) HELD BY U.S. HOLDERS OF AVENTIS

Aventis ADSs cannot be tendered by means of the enclosed forms of acceptances. These instructions and transmittal materials shall be used only if your clients are residents in the U.S. or Canada and hold Aventis ordinary shares through a French financial intermediary or through a U.S. custodian.

April 12, 2004

To French Financial Intermediaries and U.S. Custodians:

      On behalf of Sanofi-Synthelabo, a French société anonyme, we hereby inform French financial intermediaries and U.S. custodians of Sanofi-Synthelabo’s offer to exchange (i) 0.8333 of a newly ordinary share, nominal value €2 per share, of Sanofi-Synthelabo and €11.50 in cash, without interest, for each tendered ordinary share of Aventis, a French société anonyme, nominal value €3.82 per share; and (ii) 1.6667 newly issued American depositary shares, or ADSs (each ADS representing one-half of one Sanofi-Synthelabo ordinary share), of Sanofi-Synthelabo and an amount in U.S. dollars equal to €11.50 in cash, without interest, for each tendered Aventis ADS (each Aventis ADS representing one Aventis ordinary share), in each case on the terms and subject to the conditions set forth in the prospectus, dated April 9, 2004 (the “Prospectus”), and the related letter of transmittal and forms of acceptance (the “U.S. offer”).

      The U.S. offer is being made separately from (i) a French offer, which is open to holders of Aventis ordinary shares who are located in France and to holders of Aventis ordinary shares who are located outside of France, Germany and the United States, if, pursuant to the local laws and regulations applicable to those holders, they are permitted to participate in the French offer, and (ii) a German offer, which is open to holders of Aventis ordinary shares who are located in Germany. The U.S. offer, the French offer and the German offer are being made on substantially similar terms, and completion of the offers is subject to the same conditions. Terms used in this document to the extent not defined herein shall have the same meaning as in the Prospectus.

1. Aventis Securities Targeted by the U.S. Offer

      Sanofi-Synthelabo is offering to acquire all of Aventis’s issued and outstanding ordinary shares, including Aventis ordinary shares represented by Aventis ADSs, and all Aventis ordinary shares that are or may become issuable prior to the expiration of the offers due to the exercise of outstanding Aventis subscription stock options or the exercise of outstanding Aventis warrants (Bons de souscription d’actions, or BSAs).

2. Terms of the U.S. Offer

      For each Aventis ordinary share validly tendered and not withdrawn, the tendering holder will receive:

•  0.8333 of a Sanofi-Synthelabo ordinary share; and

•  €11.50 in cash, without interest.

      For each Aventis ADS (each Aventis ADS representing one Aventis ordinary share) validly tendered and not withdrawn, the tendering holder will receive:

•  1.6667 Sanofi-Synthelabo ADSs (each Sanofi-Synthelabo ADS representing one-half of one Sanofi-Synthelabo ordinary share); and

•  an amount in U.S. dollars equal to €11.50 in cash, without interest.

      The U.S. offer includes a mix and match election feature that allows holders of Aventis ordinary shares, including Aventis ordinary shares represented by Aventis ADSs, to elect to receive, in lieu of the mix of consideration described above:

•  1.0294 newly issued Sanofi-Synthelabo ordinary shares in exchange for each Aventis ordinary share tendered; or 2.0588 newly issued Sanofi-Synthelabo ADSs in exchange for each Aventis ADS tendered; or

2

•  €60.43 in cash, without interest, in exchange for each ordinary share of Aventis tendered; or an amount in U.S. dollars equal to €60.43, in cash, without interest, in exchange for each Aventis ADS tendered.

Holders are not required to make any election or to make the same election for all of the Aventis ordinary shares or Aventis ADSs that they tender. However, the mix and match elections are subject to proration and allocation adjustments that will ensure that, in the aggregate (and subject to adjustment if Aventis pays any dividend or interim dividend before the settlement of the offers), 81.0% of the Aventis ordinary shares (including Aventis ordinary shares underlying the Aventis ADSs) tendered in the U.S. offer and the concurrent French offer and German offer will be exchanged for Sanofi-Synthelabo ordinary shares (including Sanofi-Synthelabo ordinary shares underlying Sanofi-Synthelabo ADSs) and 19.0% will be purchased for cash.

      If Aventis pays any dividend or any interim dividend in respect of the Aventis ordinary shares, including Aventis ordinary shares represented by Aventis ADSs, before the settlement of the offers, the consideration offered in exchange for each Aventis ordinary share and each Aventis ADS tendered will be reduced by an amount equal to the net value of the dividend paid per Aventis ordinary share in the manner described in the Prospectus under “The U.S. Offer — Consideration Offered after Payment of Aventis Dividends”. In respect of any Sanofi-Synthelabo ordinary share, including any Sanofi-Synthelabo ordinary shares represented by Sanofi-Synthelabo ADSs, that holders receive in exchange for the Aventis ordinary shares or the Aventis ADSs that they tender in this exchange offer, such holders will be entitled to receive any annual dividend with respect to Sanofi-Synthelabo’s 2003 results that is declared on the Sanofi-Synthelabo ordinary shares and any other dividend that is paid after the settlement of this exchange offer.

      Holders of Aventis subscription stock options or warrants who wish to tender into the U.S. offer must first exercise their options or warrants and then tender the underlying Aventis ordinary shares on or prior to the expiration date of the U.S. offer according to the instructions given in the Prospectus.

      The U.S. offer will begin on April 12, 2004 and end at 5:00 p.m., New York City time, on May 28, 2004, unless: (a) the French Autorité des marchés financiers (“AMF”) sets a later expiration date for the tender period of the French offer, (b) the AMF has not at that time set an expiration date for the tender period of the French offer, (c) the AMF subsequently extends the tender period of the French offer, or (d) the offers lapse or are withdrawn prior to that time. Sanofi-Synthelabo intends that the U.S. offer, the French offer and the German offer will expire simultaneously. If the initial expiration date of the French offer is later than May 28, 2004, of if the French offer period is extended, Sanofi-Synthelabo will issue a press release announcing a corresponding extension of the U.S. offer.

      The AMF may decide to extend the offer period under certain circumstances related to, among other things, the success of the offers or the initiation of a competing offer, in which case the U.S. offer period will be likewise extended. Your clients must tender their Aventis securities before the expiration of the U.S. offer to participate.

      Aventis securityholders who want to exchange or tender their Aventis securities according to the proposed terms must submit the enclosed forms of acceptance, signed by them.

3. Fractional Shares

      No fractional Sanofi-Synthelabo ordinary shares will be issued in connection with the U.S. offer. In lieu of any fraction of a Sanofi-Synthelabo ordinary share that a holder would otherwise have been entitled to receive pursuant to the terms of the U.S. offer, such holder will receive an amount in cash equal to the product of that fraction and the average sale price per Sanofi-Synthelabo ordinary share, net of expenses, realized on Euronext Paris in the sale of all the aggregated fractional Sanofi-Synthelabo ordinary shares that would have otherwise been issued in the offers.

      No fractional Sanofi-Synthelabo ADSs will be issued in connection with the U.S. offer. In lieu of any fraction of a Sanofi-Synthelabo ADS that a holder would otherwise have been entitled to receive pursuant to the terms of the U.S. offer, such holder will receive an amount in cash equal to the product of that fraction and the average sale price per Sanofi-Synthelabo ADS, net of expenses, realized on the New York Stock Exchange (the “NYSE”) in the sale by the U.S. ADS exchange agent of all the aggregated fractional Sanofi-Synthelabo ADSs that would have otherwise been issued in the offers.

      The sale of the aggregated fractional Sanofi-Synthelabo ordinary shares on Euronext Paris and the sale of the aggregated fractional Sanofi-Synthelabo ADSs on the NYSE will occur no later than six trading days following the settlement of the offers. Payments of cash in lieu of any fractional Sanofi-Synthelabo ordinary share or fractional Sanofi-Synthelabo ADS that

3

a holder would otherwise have been entitled to receive pursuant to the terms of the U.S. offer will be paid to such holder as promptly as practicable.

      In no event will interest be paid on the cash to be received in lieu of any fraction of a Sanofi-Synthelabo ordinary share or any fraction of a Sanofi-Synthelabo ADS, regardless of any delay in making the payment.

4. Conditions to the U.S. Offer

Minimum tender condition

      Sanofi-Synthelabo will not be obligated to purchase any tendered Aventis securities pursuant to the U.S. offer unless Aventis securities representing at least 50% of the total share capital and voting rights in Aventis, calculated on a fully diluted basis, plus one Aventis ordinary share are validly tendered and not withdrawn in the U.S. offer, the French offer and the German offer, on a combined basis. This condition is referred to as the “minimum tender condition”.

      Sanofi-Synthelabo may waive the minimum tender condition at any time on or prior to the date that is five French trading days prior to the expiration date of the offers. Under French law and regulations, a waiver of the minimum tender condition is deemed an improved offer and may cause the AMF to extend the offer period and the AMF may also declare your tenders null and void. Unless we have waived the minimum tender condition, if the minimum tender condition is not satisfied the offers will lapse.

      Neither Sanofi-Synthelabo nor holders of Aventis securities will know whether the minimum tender condition has been satisfied until the results of the offers are published by the AMF following the expiration date of the offer.

     Antitrust condition

      Sanofi-Synthelabo’s obligation to complete the offers is subject to the conditions that the applicable waiting period under the U.S. Hart-Scott-Rodino Act of 1976 has expired or been terminated and no order has been entered prohibiting the transaction.

      This condition is referred to as the “antitrust condition”. Under applicable French regulations, the French offer will lapse as soon as the U.S. Federal Trade Commission issues a second request for information before the expiration of the HSR waiting period. If the French offer lapses for this reason, we will withdraw the U.S. offer and the German offer.

     Share issuance condition

      In addition, Sanofi-Synthelabo’s obligation to complete the U.S. offer is subject to the condition that the issuance of additional Sanofi-Synthelabo ordinary shares to be issued on completion of the U.S. offer, the French offer and the German offer has been duly approved by the shareholders of Sanofi-Synthelabo at an extraordinary meeting of shareholders to be held for this purpose. This condition is referred to as the “share issuance condition”.

     Sanofi-Synthelabo’s grounds for withdrawing the offers

      In accordance with French law and regulations, Sanofi-Synthelabo reserves the right to withdraw the offers:

•  within five French trading days following the date of the publication by the AMF of the offer timetable for a competing offer for Aventis or an improved offer by a competing bidder; or

•  with the prior approval of the AMF if, prior to the publication by the AMF of the definitive results of the offers, Aventis adopts definitive measures that modify Aventis’s substance (“modifiant sa consistance”) or if the offers become irrelevant (“sans objet”) under French law.

      In addition, as mentioned above, if the minimum tender condition is not satisfied, the offers will lapse.

      Under French law, if, during the period of these offers, another offer for Aventis is approved by the AMF, tenders of Aventis securities will be declared null and void by the AMF. In addition, if an improved offer by a competing bidder is approved by the AMF, tenders of Aventis securities may also be declared null and void by the AMF. In each of these events, in order to tender your Aventis securities in the U.S. offer, if the U.S. offer remains outstanding, holders will be required to re-tender their Aventis securities.

4

5. Centralization of the Orders

      You will notify Euronext Paris S.A. of the number of Aventis securities for which you received tender orders and deliver the corresponding securities to Euronext Paris S.A. according to the procedures described in the notice of Euronext Paris S.A. Model forms of acceptance to be used by holders of Aventis securities in accepting the U.S. offer and tendering Aventis securities are attached hereto.

6. Results of the Offers

      The AMF is expected to publish the definitive results of the U.S. offer, the French offer and the German offer not more than nine French trading days following the expiration date of the offers. However, if the AMF determines that the minimum tender condition has been satisfied, the AMF will publish provisional results prior to its publication of definitive results.

7.     Right to Dividends

     Dividend of Sanofi-Synthelabo

      In respect of the Sanofi-Synthelabo ordinary shares, including Sanofi-Synthelabo ordinary shares represented by Sanofi-Synthelabo ADSs, that holders receive in exchange for their Aventis securities, such holders will be entitled to receive:

•  any annual dividend that is approved to be paid with respect to Sanofi-Synthelabo’s 2003 results, and

•  any other dividend that is paid after the settlement of the offers.

      For additional details, see the Prospectus under “The U.S. Offer — Entitlement to Sanofi-Synthelabo Dividends”.

     Dividend of Aventis

      If Aventis pays any dividend or any interim dividend in respect of the Aventis ordinary shares, including Aventis ordinary shares represented by Aventis ADSs, before the settlement of the U.S. offer, the consideration offered in exchange for each Aventis ordinary share and each Aventis ADS tendered will be reduced by an amount equal to the net value of the dividend paid per Aventis ordinary share, in the manner described in the Prospectus under “The U.S. Offer — Consideration Offered after Payment of Aventis Dividends”.

8. Listing of Sanofi-Synthelabo Ordinary Shares and Sanofi-Synthelabo ADSs

      Sanofi-Synthelabo ordinary shares are currently listed and admitted to trade on Euronext Paris. Sanofi-Synthelabo ADSs are currently listed and admitted to trade on the New York Stock Exchange (the “NYSE”). Sanofi-Synthelabo has applied for the supplemental listing of the Sanofi-Synthelabo ordinary shares and Sanofi-Synthelabo ADSs to be issued in the offers on Euronext Paris and on the NYSE, as applicable.

9. Tax Regime Governing the U.S. Offer

      Please refer to the “The U.S. Offer — Material French Tax and U.S. Federal Income Tax Consequences” section in the Prospectus for a discussion of the tax implications of the U.S. offer.

10. Remuneration of the Financial Intermediaries

      Sanofi-Synthelabo will pay the brokerage fees, if any, and related value added taxes incurred by holders of Aventis securities tendering into the U.S. offer, up to a limit of 0.3% of the value of each Aventis security tendered, and subject to a maximum amount of €45 per account, including all taxes. Holders of Aventis securities will not be reimbursed for any brokerage fees in any event that the U.S. offer is withdrawn or is not completed. Financial intermediaries will be paid a fee, net of tax, of €0.20 per Aventis ordinary share, with a maximum fee of €45 per account. This fee will not be paid in the event that the U.S. offer is withdrawn or is not completed and will not be paid in any event with respect to tendered Aventis securities owned by such financial intermediaries. Any demands for the foregoing fees must be made in writing on or prior to the date that is five days following the expiration date.

5

      Your prompt action is requested. We urge you to contact your clients as promptly as possible. The U.S. offer and withdrawal rights will expire at 5:00 p.m., on May 28, 2004, unless extended. You should forward a copy of the Prospectus to your U.S. clients.

      Any inquiries that you have with respect to the U.S. offer should be addressed to MacKenzie Partners, Inc., the information agent, at 105 Madison Avenue, New York, New York 10016, (212) 929-5500. You may request copies of the Prospectus from the information agent.

Very truly yours,

MERRILL LYNCH & CO.

BNP PARIBAS

6 EX-99.A.1.VIII 10 e93031exv99waw1wviii.htm LETTER TO CLIENTS

Exhibit (a)(1)(viii)

Aventis ADSs cannot be tendered by means of the enclosed forms of acceptance. These transmittal materials shall be used only if you hold Aventis ordinary shares through a French financial intermediary or through a U.S. custodian.

U.S. OFFER TO EXCHANGE

All Ordinary Shares, including

Ordinary Shares Represented by American Depositary Shares

of

Aventis

Pursuant to the prospectus, dated April 9, 2004

by

Sanofi-Synthelabo

THE U.S. OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 5:00 P.M., NEW YORK CITY TIME, ON MAY 28, 2004, UNLESS THE U.S. OFFER IS EXTENDED OR IS WITHDRAWN PRIOR TO THAT TIME.

April 12, 2004

To Our Clients:

      Enclosed for your consideration are certain forms of acceptance (each, a “form of acceptance”) in connection with the offer by Sanofi-Synthelabo, a French société anonyme, to exchange (a) each American depositary share (“ADS”) of Aventis, a French société anonyme, for 1.6667 Sanofi-Synthelabo ADSs (each Sanofi-Synthelabo ADS representing one-half of one Sanofi-Synthelabo ordinary share) and an amount in cash in U.S. dollars equal to €11.50 and (b) each Aventis ordinary share (other than Aventis ordinary shares represented by Aventis ADSs) for 0.8333 of a Sanofi-Synthelabo ordinary share and an amount in cash in U.S. dollars equal to €11.50, in each case on the terms and subject to the conditions set forth in the prospectus, dated April 9, 2004 (the “prospectus”), the related ADS letter of transmittal and notice of guaranteed delivery (which, as amended or supplemented from time to time, constitute the “U.S. offer”). Terms used in this document to the extent not defined herein shall have the same meaning as in the prospectus.

      We are (or our nominee is) the holder of record of Aventis ordinary shares held by us for your account. A tender of such Aventis ordinary shares can be made only by us as the holder of record and pursuant to your instructions.

      Accordingly, we request instructions as to whether you wish to have us tender on your behalf any or all of the Aventis ordinary shares held by us for your account, pursuant to the terms and conditions set forth in the prospectus. The prospectus and any additional information can be obtained from the information agent for the U.S. offer, MacKenzie Partners, Inc., at 105 Madison Avenue, New York, New York 10016, (800) 322-2885 (toll free).

      Your attention is directed to the following:

      1.     The U.S. offer is to exchange (a) each Aventis ADS for 1.6667 Sanofi-Synthelabo ADSs (each Sanofi-Synthelabo ADS representing one-half of one Sanofi-Synthelabo ordinary share) and an amount in cash in U.S. dollars equal to €11.50 and (b) each Aventis ordinary share (other than Aventis ordinary shares represented by Aventis ADSs) for 0.8333 of a Sanofi-Synthelabo ordinary share and an amount in cash in U.S. dollars equal to €11.50, in each case on the terms and subject to the conditions set forth in the prospectus.

      The U.S. offer contains a mix and match election, whereby holders of Aventis ordinary shares and holders of Aventis ADSs may elect to receive for each of their tendered Aventis ordinary shares or Aventis ADSs, as applicable, either (a) all Sanofi-Synthelabo ordinary shares or Sanofi-Synthelabo ADSs, as applicable, or (b) all cash. Specifically, the mix and match election permits holders to receive, in lieu of the standard entitled described above:

•  1.0294 Sanofi-Synthelabo ordinary shares in exchange for each Aventis ordinary share tendered; or 2.0588 Sanofi-Synthelabo ADSs in exchange for each Aventis ADS tendered; or

•  €60.43 in cash, without interest, in exchange for each ordinary share of Aventis tendered; or an amount in U.S. dollars equal to €60.43, in cash, without interest, in exchange for each Aventis ADS tendered.

      The mix and match elections are subject to proration and allocation adjustments that will ensure that, in the aggregate, 81.0% of the Aventis ordinary shares (including Aventis ordinary shares underlying the Aventis ADSs) tendered in the U.S. offer and the concurrent French offer and German offer will be exchanged for Sanofi-Synthelabo ordinary shares (including Sanofi-Synthelabo ordinary shares underlying Sanofi-Synthelabo ADSs) and 19.0% will be purchased for cash.

      Holders are not required to make any election or to make the same election for all of the Aventis ordinary shares or Aventis ADSs that they tender. Tendering holders who wish to make a mix and match election may do so by submitting the mix and match election form to the U.S. ADS exchange agent prior to the expiration of the U.S. offer. Tendering holders who have not properly completed and submitted a mix and match election form prior to that time will receive the standard entitlement. Holders who make a mix and match election will not be informed of the exact number of Sanofi-Synthelabo ordinary shares or Sanofi-Synthelabo ADSs or the amount of cash they will receive until settlement of the consideration under the U.S. offer.

      2.     The U.S. offer is being made for all outstanding Aventis ordinary shares held by U.S. holders (within the meaning of Rule 14d-1(d) under the Securities Exchange Act) and all outstanding Aventis ADSs. Sanofi-Synthelabo will, upon the terms and subject to the conditions of the U.S. offer, exchange the Aventis ordinary shares and Aventis ADSs validly tendered and not withdrawn before the expiration date of the U.S. offer. The term “expiration date” means 5:00 p.m., New York City time, on May 28, 2004, or, if the U.S. offer is extended, the latest time and date at which the U.S. offer, as so extended by Sanofi-Synthelabo, will expire.

      3.     This U.S. offer is being made on substantially the same terms as an offer for all Aventis ordinary shares being made in France (the “French offer”) and in Germany (the “German offer”) (to the extent permitted by law and regulations), and Sanofi-Synthelabo will not be required to complete this U.S. offer unless the French offer and the German offer are completed. Sanofi-Synthelabo’s obligation to accept Aventis ordinary shares and Aventis ADSs in this U.S. offer is also subject to several conditions, including the condition that securities representing at least 50% of the total share capital and voting rights in Aventis, calculated on a fully diluted basis, plus one Aventis ordinary share are validly tendered and not properly withdrawn in the U.S. offer, the French offer and the German offer, on a combined basis (the “minimum share condition”).

      4.     The U.S. offer and withdrawal rights will expire on the expiration date, which will be 5:00 p.m., New York City time, on May 28, 2004, unless: (a) the French Autorité des marchés financiers (“AMF”) sets a later expiration date for the tender period of the French offer, (b) the AMF has not at that time set an expiration date for the tender period of the French offer, (c) the AMF subsequently extends the tender period of the French offer, or (d) the offers lapse or are withdrawn prior to that time. Sanofi-Synthelabo intends that the U.S. offer, the French offer and the German offer will expire simultaneously. If the initial expiration date of the French offer is later than May 28, 2004, or if the French offer period is extended, Sanofi-Synthelabo will issue a press release announcing a corresponding extension of the U.S. offer.

      5.     Exchange of Aventis ordinary shares tendered and accepted for exchange pursuant to the U.S. offer will be made only after timely receipt by the French financial intermediary if your Aventis ordinary shares are held through a French financial intermediary, or by the U.S. custodian if your Aventis ordinary shares are held through a U.S. custodian (each of the French financial intermediary or U.S. custodian referred to hereafter as a “Financial Intermediary”) of a properly completed and duly executed form of acceptance (or facsimile thereof) and any other documents required by the form of acceptance.

      6.     If you hold Aventis ordinary shares in pure registered (nominatif pur) form, you cannot tender them unless you first request that they be converted to administered registered (nominatif administre) form. If you wish to tender such securities, you must first make the necessary arrangements for such conversion with your Financial Intermediary.

2

      7.     Sanofi-Synthelabo will pay the brokerage fees, if any, and related value added taxes incurred by holders of Aventis securities tendering into the U.S. offer, up to a limit of 0.3% of the value of each Aventis security tendered, and subject to a maximum amount of €45 per account, including all taxes. Holders of Aventis securities will not be reimbursed for any brokerage fees in any event that the U.S. offer is withdrawn or is not completed. Financial intermediaries will be paid a fee, net of tax, of €0.20 per Aventis ordinary share, with a maximum fee of €45 per account. This fee will not be paid in the event that the U.S. offer is withdrawn or is not completed and will not be paid in any event with respect to tendered Aventis securities owned by such financial intermediaries. Any demands for the foregoing fees must be made in writing on or prior to the date that is five days following the expiration date.

      8.     Sanofi-Synthelabo will be deemed to have accepted for exchange all validly tendered and not withdrawn Aventis ordinary shares on the expiration date subject only to the satisfaction of the minimum share condition and the other conditions described in the prospectus. The AMF is expected to publish the results of the offers not later than nine French trading days following the expiration date of the offer period. However, upon determination that the minimum tender condition has been met, the AMF will publish provisional results prior to its publication of the definitive results. If the conditions are not satisfied, Sanofi-Synthelabo will promptly return all tendered Aventis securities without acquiring them.

      9.     Sanofi-Synthelabo expects that the delivery of any cash for tendered Aventis ordinary shares or Aventis ADSs will occur approximately 12 to 18 French trading days after the expiration date. Under no circumstances will interest be paid on the exchange of Aventis ordinary shares or Aventis ADSs tendered, regardless of any delay in making the exchange or extension of the expiration date. The cash consideration paid to holders tendering Aventis ordinary shares or Aventis ADSs will be paid in U.S. dollars, converted at a then current spot exchange rate, and distributed, net of expenses, to such holders. For further information, see “The U.S. Offer” in the prospectus.

      10.     Aventis ADS holders who fail to complete and sign the Substitute Form W-9 may be subject to U.S. federal income tax backup withholding at a rate of 28%. See Instruction 13 of the relevant form of acceptance.

      If you wish to have us tender any or all of the Aventis ordinary shares held by us for your account, please so instruct us by completing, executing and returning to us the instruction form set forth below. If you authorize the tender of your Aventis ordinary shares, all such Aventis ordinary shares will be tendered unless otherwise specified on the instruction form set forth below. Please forward your instructions to us as soon as possible to allow us ample time to tender Aventis ordinary shares on your behalf prior to the expiration of the U.S. offer.

      The U.S. offer is made solely by the prospectus and is being made to all U.S. holders of Aventis ordinary shares and all holders of Aventis ADSs. If Sanofi-Synthelabo becomes aware of any valid state or provincial statute prohibiting the making of the U.S. offer or the acceptance of Aventis ordinary shares pursuant thereto, Sanofi-Synthelabo will make a good-faith effort to comply with such state or provincial statute. If, after such good faith effort, Sanofi-Synthelabo cannot comply with such state or provincial statute, the U.S. offer will not be made to (nor will tenders be accepted from or on behalf of) the holders of Aventis ordinary shares in such state or province. The U.S. offer is not being made to, nor will tenders be accepted from, or on behalf of, holders of Aventis ordinary shares or holders of Aventis ADSs in any jurisdiction in which the making or acceptance of the U.S. offer would not be in compliance with the laws of such jurisdiction. In any jurisdiction where the securities or blue sky laws require the U.S. offer to be made by a licensed broker or dealer, the U.S. offer will be deemed made on behalf of Sanofi-Synthelabo by the dealer manager for the U.S. offer, or one or more registered brokers or dealers that are licensed under the laws of such jurisdiction.

3

INSTRUCTIONS WITH RESPECT TO THE

U.S. OFFER TO EXCHANGE

All Ordinary Shares, including

Ordinary Shares Represented by American Depositary Shares

of

AVENTIS

Pursuant to the Prospectus, dated April 9, 2004

by

SANOFI-SYNTHELABO

      The undersigned acknowledge(s) receipt of your letter enclosing the related form of acceptance in connection with the offer by Sanofi-Synthelabo to acquire all the issued and outstanding Aventis ordinary shares and Aventis ADSs. The undersigned acknowledges that such person has received and reviewed the prospectus, dated April 9, 2004 (the “prospectus”).

      This will instruct you to tender the number of Aventis ordinary shares indicated below (or, if no number is indicated below, all Aventis ordinary shares) that are held by you for the account of the undersigned, on the terms and subject to the conditions set forth in the prospectus and in the related form of acceptance.

      The undersigned understands and acknowledges that all questions as to validity, form and eligibility of the surrender of any Aventis ordinary shares submitted on my behalf to the Financial Intermediary will be determined by Sanofi-Synthelabo (which may delegate power in whole or in part to the Financial Intermediary) and such determination shall be final and binding.

Number of Aventis ordinary shares to be Tendered*

Dated:           , 2004
Mix and Match Election: (Complete only if you would like to exercise the mix and match election)
	Enter the number of Aventis ordinary shares for which you would like to make a mix and match election.	1
	Enter the number of Aventis ordinary shares for which you would like to receive 1.0294 Sanofi-Synthelabo ordinary shares per tendered Aventis ordinary share.	2A
	Enter the number of Aventis ordinary shares for which you would like to receive €60.43 in cash, without interest, per tendered Aventis ordinary share.	2B
	Note: The sum of the number in Box 2A and the number in Box 2B must equal the number in Box 1.

4

SIGN HERE

Signature(s)

Please Print Name

Account Number

Address

Area Code and Telephone Number

Taxpayer Identification or Social Security Number(s)

*  Unless otherwise indicated, you are deemed to have instructed us to tender all Aventis ordinary shares held by us for your account.

PLEASE RETURN THIS FORM TO THE FINANCIAL INTERMEDIARY MAINTAINING YOUR ACCOUNT.

5 EX-99.A.5.III 11 e93031exv99waw5wiii.htm TEXT OF NEWSPAPER ADVERTISEMENT DATED 4/12/04

Exhibit (a)(5)(iii)

This announcement is neither an offer to purchase or exchange nor a solicitation of an offer to sell or exchange Aventis
ordinary shares or Aventis ADSs (collectively, “Aventis securities”). The U.S. Offer (as defined below) is made
solely by the Prospectus (as defined below), the related ADS Letter of Transmittal, the related Form of
Acceptance and any amendments or supplements thereto, and is being made to all holders of Aventis
ordinary shares who are located in the United States and to all holders of Aventis ADSs, wherever
located. The U.S. Offer is not being made to, nor will Aventis securities be accepted from or on
behalf of, holders of Aventis securities in any jurisdiction in which the making of the U.S. Offer
or the acceptance thereof would not be in compliance with applicable law. In U.S. jurisdic-
tions where the applicable laws require that the U.S. Offer be made by a licensed broker
or dealer, the U.S. Offer shall be deemed to be made on behalf of Sanofi-Synthelabo
by Merrill Lynch &Co. and BNP Paribas Securities Corp., as joint dealer-
managers, or one or more registered brokers or dealers licensed
under the laws of such jurisdiction.

Sanofi-Synthelabo

Notice of Offer to Exchange

0.8333 of an ordinary share of Sanofi-Synthelabo and €11.50 in cash,

for

Each Outstanding Ordinary Share
(held by holders who are located in the United States)

of

Aventis

and

1.6667 American Depositary Shares of Sanofi-Synthelabo and
an amount in U.S. dollars equal to €11.50 in cash,

for
Each Outstanding American Depositary Share
(held by holders wherever located)
of
Aventis

     Sanofi-Synthelabo, a French société anonyme, is offering to exchange all outstanding ordinary shares, nominal value €3.82 per share, of Aventis, a French société anonyme, including Aventis ordinary shares represented by American depositary shares (“ADSs”), on the terms and subject to the conditions set forth in the prospectus, dated April 9, 2004 (the “Prospectus”), the related ADS Letter of Transmittal and the related Form of Acceptance (which collectively constitute the “U.S. Offer”). In the U.S. Offer, Sanofi-Synthelabo will exchange:

• 0.8333 of a newly issued Sanofi-Synthelabo ordinary share, nominal value €2 per share, and €11.50 in cash, without interest, for each validly tendered Aventis ordinary share; and

• 1.6667 newly issued Sanofi-Synthelabo ADSs (each Sanofi-Synthelabo ADS representing one-half of one Sanofi-Synthelabo ordinary share) and an amount in U.S. dollars equal to €11.50 in cash, without interest, for each validly tendered Aventis ADS (each Aventis ADS representing one Aventis ordinary share).

     The U.S. Offer includes a mix and match election feature that allows holders of Aventis ordinary shares, including Aventis ordinary shares represented by Aventis ADSs, to elect to receive, in lieu of the mix of consideration described above:

• 1.0294 newly issued Sanofi-Synthelabo ordinary shares in exchange for each Aventis ordinary share tendered; or 2.0588 newly issued Sanofi-Synthelabo ADSs in exchange for each Aventis ADS tendered; or

• €60.43 in cash, without interest, in exchange for each ordinary share of Aventis tendered; or an amount in U.S. dollars equal to €60.43, in cash, without interest, in exchange for each Aventis ADS tendered.

     The mix and match elections are subject to proration and allocation adjustments that will ensure that, in the aggregate (and subject to adjustment if Aventis pays any dividend or interim dividend before the settlement of the Offers, as defined below), 81.0% of the Aventis ordinary shares (including Aventis ordinary shares underlying the Aventis ADSs) tendered in the U.S. Offer and the concurrent French Offer (defined below) and concurrent German Offer (defined below) will be exchanged for Sanofi-Synthelabo ordinary shares (including Sanofi-Synthelabo ordinary shares underlying Sanofi-Synthelabo ADSs) and 19.0% will be purchased for cash.

     If Aventis pays any dividend or any interim dividend in respect of the Aventis ordinary shares, including Aventis ordinary shares represented by Aventis ADSs, before the settlement of the Offers, the consideration offered in exchange for each Aventis ordinary share and each Aventis ADS tendered will be reduced by an amount equal to the net value of the dividend paid per Aventis ordinary share. In respect of any Sanofi-Synthelabo ordinary share, including any Sanofi-Synthelabo ordinary shares represented by Sanofi-Synthelabo ADSs, that a holder receives in exchange for the Aventis ordinary shares or the Aventis ADSs that such holder tenders in the U.S. Offer, such holder will be entitled to receive any annual dividend with respect to Sanofi-Synthelabo’s 2003 results that is declared on the Sanofi-Synthelabo ordinary shares and any other dividend that is paid after the settlement of the U.S. Offer.

     No fractional Sanofi-Synthelabo ordinary share or fractional Sanofi-Synthelabo ADS will be issued in connection with the U.S. Offer. Instead, any holder that would otherwise be entitled to a fraction of a Sanofi-Synthelabo ordinary share or Sanofi-Synthelabo ADS will receive an amount in cash equal to the product of that fraction and the average sale price per Sanofi-Synthelabo ordinary share, net of expenses, realized on Euronext Paris or the average sale price per Sanofi-Synthelabo ADS, net of expenses, realized on the New York Stock Exchange (“NYSE”), as applicable, in the sale of all of the aggregated fractional Sanofi-Synthelabo ordinary shares or all of the aggregated fractional Sanofi-Synthelabo ADSs that would otherwise have been issued in the Offers.

     The U.S. Offer, which is open to all holders of Aventis ordinary shares who are located in the United States and to all holders of Aventis ADSs, wherever located, is being made separately from (i) a French offer (the “French Offer”), which is open to all holders of Aventis ordinary shares who are located in France and to holders of Aventis ordinary shares who are located outside of France, Germany and the United States, if, pursuant to the local laws and regulations applicable to such holders, they are permitted to participate in the French Offer; and (ii) a German offer (the “German Offer”), which is open to holders of Aventis ordinary shares who are located in Germany. Together, the U.S. Offer, the French Offer and the German Offer (collectively, the “Offers”) are being made for all issued and outstanding Aventis ordinary shares, including Aventis ordinary shares represented by Aventis ADSs, and all Aventis ordinary shares that are or may become issuable prior to the expiration of the Offers due to the exercise of outstanding Aventis stock options or the exercise of outstanding Aventis warrants (Bons de souscription d’actions, or BSAs). The Offers are being made on substantially similar terms and completion of the Offers is subject to the same conditions.

     Sanofi-Synthelabo will pay the brokerage fees, if any, and related value added taxes incurred by holders of Aventis securities tendering into the U.S. Offer, up to a limit of 0.3% of the value of each Aventis security tendered, and subject to a maximum amount of €45 per account, including all taxes. Holders of Aventis securities will not be reimbursed for any brokerage fees in the event that the U.S. Offer is withdrawn or is not completed. Financial intermediaries will be paid a fee, net of tax, of €0.20 per Aventis ordinary share, with a maximum fee of €45 per account. This fee will not be paid in the event that the U.S. Offer is withdrawn or is not completed and will not be paid in any event with respect to tendered Aventis securities owned by such financial intermediaries. Sanofi-Synthelabo will pay any stamp duty (impôt de bourse) provided by article 978 of the French tax code (Code général des impôts) with respect to Aventis ordinary shares tendered pursuant to an all-cash election. Sanofi-Synthelabo will pay or cause to be paid any transfer taxes with respect to the exchange of Aventis ADSs not based on income.

     Sanofi-Synthelabo will pay the fees charged by the ADS depositary for Aventis ADSs tendered into the U.S. Offer, including any fees charged by the ADS depositary to redeposit Aventis ordinary shares underlying tendered Aventis ADSs that have been previously withdrawn from deposit with the ADS depositary in the event that the Offers are not consummated. Sanofi-Synthelabo will pay all charges and expenses of The Bank of New York, which is acting on behalf of Sanofi-Synthelabo as exchange agent for the Aventis ADSs (the “U.S. ADS Exchange Agent”), MacKenzie Partners, Inc., which is acting as the information agent (the “Information Agent”), and Merrill Lynch & Co. and BNP Paribas Securities Corp., which are acting as joint dealer-managers (the “Joint Dealer-Managers”), incurred in connection with the U.S. Offer.

     THE U.S. OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 5:00 P.M., NEW YORK CITY TIME, ON MAY 28, 2004, UNLESS THE U.S. OFFER IS EXTENDED OR IS WITHDRAWN PRIOR TO THAT TIME. YOU MAY WITHDRAW ANY AVENTIS SECURITIES TENDERED AT ANY TIME PRIOR TO THE EXPIRATION TIME.

     Sanofi-Synthelabo’s obligation to complete the Offers is subject to the following conditions: (1) at least 50% of the total share capital and voting rights in Aventis, calculated on a fully diluted basis, plus one Aventis ordinary share are validly tendered and not withdrawn in the U.S. Offer, the French Offer and the German Offer, on a combined basis (the “minimum tender condition”); (2) the applicable waiting period under the U.S. Hart-Scott-Rodino Act of 1976 (“HSR”) has expired or been terminated and no order has been entered prohibiting the transaction (the “antitrust condition”); and (3) the issuance of additional Sanofi-Synthelabo ordinary shares to be issued on completion of the Offers has been duly approved by the shareholders of Sanofi-Synthelabo at an extraordinary meeting of shareholders to be held for this purpose (the “share issuance condition”). Sanofi-Synthelabo may waive the minimum tender condition at any time on or prior to the date that is five French trading days prior to the expiration date of the Offers. Under French law and regulations, a waiver of the minimum tender condition is deemed an improved Offer and may cause the French Autorité des marchés financiers (the “AMF”) to extend the Offer period; the AMF may also declare any tenders null and void. If the minimum tender condition is not satisfied, the Offers will not be completed. Because the Offers are subject to the antitrust condition, under applicable French law, the French Offer will lapse (“est caduque”, meaning it is null and void) as soon as the U.S. Federal Trade Commission issues a second request for information before the expiration of the HSR waiting period. If the French Offer lapses for this reason, Sanofi-Synthelabo will withdraw the U.S. Offer and the German Offer. At the meeting of the board of directors of Sanofi-Synthelabo, representatives of Total and L’Oréal, which are Sanofi-Synthelabo’s two principal shareholders (holding, as of December 31, 2003, an aggregate of 47.1% of Sanofi-Synthelabo’s outstanding share capital (other than share capital held by Sanofi-Synthelabo) and 63.1% of Sanofi-Synthelabo’s voting rights), confirmed their full support of the Offers. Total and L’Oréal have also expressed that they will approve the increase in share capital that will be submitted to the extraordinary meeting of shareholders. If the Offers are not completed because a condition is not satisfied, or the French Offer lapses and Sanofi-Synthelabo withdraws the U.S. Offer and the German Offer, Sanofi-Synthelabo reserves the right to commence a new offer or not, in its sole discretion, and to make that offer available in the United States or not, in its sole discretion. If the Offers are not successful, or the French Offer lapses and Sanofi-Synthelabo withdraws the U.S. Offer and the German Offer, the Aventis securities tendered in the U.S. Offer will be returned to tendering holders of Aventis securities, without interest or any other payment being due. This should occur within one or two French trading days following the announcement of the lapse, withdrawal or failure of the Offers.

     The U.S. Offer will expire at 5:00 p.m., New York City time, on May 28, 2004, unless (1) the AMF sets a later expiration date for the tender period of the French Offer, (2) the AMF has not set an expiration date for the French Offer by May 28, 2004, (3) the AMF subsequently extends the tender period of the French Offer, or (4) the Offers lapse or are withdrawn prior to that time. Sanofi-Synthelabo intends that the U.S. Offer, the French Offer and the German Offer will all expire simultaneously. Under French tender offer rules, the AMF sets the expiration date of the French Offer and has the sole authority to determine whether or not to subsequently extend the French tender period. In connection with the appeals by Aventis of the AMF’s clearance decision (avis de recevabilité) and the AMF’s decision to grant a visa for Sanofi-Synthelabo’s French Offer prospectus, the AMF has undertaken to set the expiration date of the French Offer to be at least eight days after the Court of Appeals of Paris announces its decision on the appeals by Aventis. The AMF may decide subsequently to extend the initial French tender period under certain circumstances, including in the event of the initiation of a competing offer or of an improved offer by a competing bidder. If the AMF (1) sets an initial expiration date for the French Offer that is later than May 28, 2004, or (2) subsequently extends the initial French tender period, Sanofi-Synthelabo will, on the same day, issue a press release announcing the AMF’s decision and a corresponding extension of the U.S. Offer. Sanofi-Synthelabo’s press release will set forth the expiration date and time of the extended U.S. Offer and inform holders of Aventis securities subject to the U.S. Offer that they may tender, or withdraw their tendered, Aventis securities at any time until the expiration of the extended offer period.

     The AMF is expected to publish the definitive results of the Offers not more than nine French trading days following the expiration date of the Offers. However, upon determination that the minimum tender condition has been satisfied, the AMF will publish provisional results prior to its publication of the definitive results.

     If as a result of the U.S. Offer, the French Offer and the German Offer, Sanofi-Synthelabo acquires in aggregate between two-thirds and 95% of Aventis’s total share capital and voting rights, or more than 50% if there is a concurrent competing offer for Aventis securities, Sanofi-Synthelabo intends to provide a subsequent offering period of at least 10 French trading days as permitted under the rules governing the French Offer. If Sanofi-Synthelabo provides a subsequent offering period in the French Offer, it will provide a subsequent offering period in the U.S. Offer and the German Offer. If Sanofi-Synthelabo meets the conditions for a subsequent offering period, Sanofi-Synthelabo will announce its intention at the same time that it announces the results of the Offers, which Sanofi-Synthelabo will do by issuing a press release as soon as practicable (but in no event later than 10 French trading days) after the AMF publishes definitive results of the Offers. The AMF will then set and publish the calendar for such a subsequent offering period, which would ordinarily begin within a few days following the publication by the AMF of the timetable. In the event of a subsequent offering period, Sanofi-Synthelabo will offer the same consideration that was offered during the initial offering period.

     Holders of Aventis ADSs held in certificate form, commonly known as American depositary receipts (“ADRs”), may tender such Aventis ADSs in the U.S. Offer by delivering prior to the expiration date the following materials to the U.S. ADS Exchange Agent at one of its addresses set forth on the back cover of the Prospectus: (1) their Aventis ADRs, (2) a properly completed and duly executed ADS Letter of Transmittal, or a facsimile copy with an original manual signature, with any required signature guarantees, and (3) any other documents required by the ADS Letter of Transmittal. Holders of Aventis ADSs held in book-entry form may tender such Aventis ADSs in the U.S. Offer by taking the following actions prior to the expiration date: (A) a book-entry transfer of such Aventis ADSs into the U.S. ADS Exchange Agent’s account at the Depository Trust Company (“DTC”), (B) delivery to the U.S. ADS Exchange Agent at one of its addresses set forth on the back cover of the Prospectus of either (1) a properly completed and duly executed ADS Letter of Transmittal, or a facsimile copy with an original manual signature, with any required signature guarantees, or (2) an agent’s message (as defined in the Prospectus), and (C) delivery to the U.S. ADS Exchange Agent at one of its addresses set forth on the back cover of the Prospectus of any other documents required by the ADS Letter of Transmittal. Aventis ordinary shares held through a French financial intermediary may be tendered pursuant to the U.S. Offer only by completing the relevant Form of Acceptance and other transmittal materials sent by the French financial intermediary and pursuant to the instructions for participating in the U.S. Offer. Aventis ordinary shares held through a U.S. custodian may be tendered pursuant to the U.S. Offer only by completing the relevant Form of Acceptance and other transmittal materials sent by the U.S. custodian pursuant to instructions for participating in the U.S. Offer. Aventis ordinary shares may not be tendered by completing the ADS Letter of Transmittal. In addition, tendering holders of Aventis ordinary shares held in pure registered (nominatif pur) form will not be able to tender the Aventis ordinary shares pursuant to the U.S. offer unless such Aventis ordinary shares are first converted to administered registered (nominatif administré) form or bearer form (au porteur) as described in the Prospectus. All questions as to the validity, form and eligibility for exchange of any tendered Aventis securities will be determined by Sanofi-Synthelabo, in its discretion, and its determination will be final and binding on the holders of the Aventis securities.

     Tenders of Aventis securities made pursuant to the U.S. Offer may be withdrawn at any time prior to the expiration of the U.S. Offer. If a subsequent offering period is provided, Aventis securities tendered during that subsequent period may be withdrawn at any time prior to the expiration of such subsequent period. For a withdrawal to be effective, the French financial intermediary, the U.S. custodian or the U.S. ADS Exchange Agent, as applicable, must receive in a timely manner the written or facsimile transmission notice of withdrawal. Any such

notice must specify the name of the person who tendered the Aventis securities being withdrawn, the number of Aventis securities being withdrawn and the name of the registered holder, if different from that of the person who tendered such Aventis securities. If Aventis ADRs being withdrawn have been delivered or otherwise identified to the U.S. ADS Exchange Agent, then, prior to the physical release of such ADRs, (1) the U.S. ADS Exchange Agent also must receive the name of the registered holder and the serial numbers of the particular Aventis ADRs and (2) the signature(s) on the notice of withdrawal must be guaranteed by an eligible institution unless such Aventis ADSs have been tendered for the account of an eligible institution. If Aventis ADSs have been tendered pursuant to the procedure for book-entry transfer, any notice of withdrawal must specify the name and number of the account at DTC to be credited with the withdrawal of Aventis ADSs. If tendered Aventis ordinary shares are being withdrawn, the notice of withdrawal must specify the name and number of the Euroclear France account to be credited with the withdrawn Aventis securities. All questions as to the form and validity (including time of receipt) of any notice of withdrawal will be determined by Sanofi-Synthelabo, in its sole discretion, and its determination will be final and binding on the holders of the Aventis securities.

     If the Offers are successful, Sanofi-Synthelabo securities and cash will be delivered to tendering holders of Aventis securities following the publication by the AMF of the final results of the Offers. Settlement is currently expected to take place approximately 12 to 18 French trading days following the expiration date of the Offers. Similarly, in the event of a subsequent offering period, if any, settlement is expected to occur within 12 to 18 French trading days following the expiration of that subsequent offer period. With respect to tendered Aventis ADSs only, the cash consideration payable in the U.S. Offer will be paid in U.S. dollars calculated by converting the applicable amount in euros into U.S. dollars using a current spot exchange rate, less expenses. Sanofi-Synthelabo ADSs to be evidenced by ADRs registered in the name of the tendering holder may not be delivered until approximately two weeks after the settlement date.

     Sanofi-Synthelabo’s acquisition of the Aventis securities will be accounted for using the purchase method under both French GAAP and U.S. GAAP.

     If a tendering holder is a non-resident of France and not a member of a special class of taxpayers (as described in the Prospectus under “Material French Tax and U.S. Federal Income Tax Consequences”) for French tax purposes, such holder will not be subject to French tax on any capital gain or loss recognized, for French tax purposes, as a result of exchanging such holder’s Aventis securities pursuant to the U.S. Offer, unless such holder has a permanent establishment or fixed base in France and the Aventis securities exchanged are part of the business property of that permanent establishment or fixed base. For French tax purposes, the gain or loss, if any, will equal the difference between (a) the fair market value of the Sanofi-Synthelabo ordinary shares or ADSs plus the amount of cash that such holder receives in the exchange and (b) such holder’s adjusted tax basis in the Aventis securities that such holder exchanges.

     If a tendering holder is a U.S. holder (as defined in the Prospectus under “Material French Tax and U.S. Federal Income Tax Consequences”) and is not a member of a special class of taxpayers (as described in the Prospectus under “Material French Tax and U.S. Federal Income Tax Consequences”) for U.S. federal income tax purposes, as a result of exchanging Aventis securities pursuant to the U.S. Offer, such holder will generally recognize gain or loss, if any, for United States federal income tax purposes in an amount equal to the difference between (a) the fair market value of the Sanofi-Synthelabo securities plus the amount of cash that such holder receives in the exchange and (b) such holder’s adjusted tax basis in such Aventis securities exchanged. For U.S. federal income tax purposes, in general, if a holder is a non-U.S. holder, such holder will not be subject to United States federal income taxation on any gain or loss recognized in exchanging such holder’s Aventis securities. Exceptions are described in more detail in the Prospectus under “Material French Tax and U.S. Federal Income Tax Consequences — Tax Consequences of Exchanging Aventis Securities — United States federal income taxation — Non-U.S. Holders”.

     The information required to be disclosed by Rule 14d-6(d)(1) of the General Rules and Regulations under the Securities Exchange Act of 1934 (the “Exchange Act Rules”) is contained in the Prospectus and is incorporated herein by reference. In connection with the U.S. Offer, Sanofi-Synthelabo has delivered a written request to Aventis pursuant to Rule 14d-5 of the Exchange Act Rules relating to the use of Aventis’s stockholder lists and security position listings. The Prospectus, the related ADS Letter of Transmittal, the related Form of Acceptance and other related materials will be mailed to registered holders of Aventis ADSs and to registered holders of Aventis ordinary shares in the United States and will be furnished to brokers, dealers, commercial banks, trust companies and similar persons whose names, or the names of whose nominees, appear on the stockholder list or, if applicable, who are listed as participants in a clearing agency’s security position listing for subsequent transmittal to beneficial owners of Aventis securities.

     The Prospectus, the related ADS Letter of Transmittal and the related Form of Acceptance contain important information that should be read carefully before any decision is made with respect to the U.S. Offer.

     Any questions or requests for assistance or for additional copies of the Prospectus, the related ADS Letter of Transmittal, the related Form of Acceptance and other related tender offer materials may be directed to the Information Agent at its address and telephone number set forth below, and copies will be furnished promptly at Sanofi-Synthelabo’s expense.

The Information Agent for the U.S. Offer is:

105 Madison Avenue
New York, New York 10016

(212) 929-5500 (Call Collect)
or
CALL TOLL-FREE (800) 322-2885
E-mail: proxy@mackenziepartners.com

The Joint Dealer Managers for the U.S. Offer are:

Four World Financial Center	The Equitable Tower, 787 Seventh Avenue
New York, New York 10080	New York, New York 10019
Toll-Free Call: (866) 276-1462	(212) 841-3700

April 12, 2004

EX-99.A.1.VIII

LETTER TO CLIENTS

EX-99.A.5.III

TEXT OF NEWSPAPER ADVERTISEMENT DATED 4/12/04