For registration of certain classes of securities
pursuant to Section 12(b) or (g) of the
Securities Exchange Act of 1934

Massachusetts (State of Incorporation or Organization)		06-1047163 (I.R.S. Employer Identification No.)
500 Kendall Street, Cambridge, Massachusetts (Address of Principal Executive Offices)		02142 (Zip Code)

Title of Each Class to be so Registered
None

Name of Each Exchange on which Each Class is to be Registered
None

If this form relates to the registration of a class of securities pursuant to Section 12(b) of the Exchange Act and is effective pursuant to General Instruction A.(c), check the following box. o

If this form relates to the registration of a class of securities pursuant to Section 12(g) of the Exchange Act and is effective pursuant to General Instruction A.(d), check the following box. ý

Securities Act registration statement file number to which this form relates: (if applicable).

The purpose of this Amendment No. 3 is to revise the description of rights to purchase Genzyme's common stock $0.01 par value per share (which have been previously registered pursuant to section 12(g) of the Exchange Act of 1934, as amended), to reflect the amendment to Genzyme's Revised Articles of Organization, filed on the date hereof, which provides that shares of Genzyme General Division Common Stock no longer carry such designation and now represent the only authorized series of Genzyme common stock.

Pursuant to the Fourth Amended and Restated Renewed Rights Agreement dated as of May 28, 2004 between Genzyme and American Stock Transfer & Trust Company, as Rights Agent (the "Amended Rights Agreement"), each outstanding share of Common Stock also represents one common stock purchase right (a "Right"). Each Right, upon becoming exercisable, will entitle the holder to buy one two-hundredth of a newly-issued share of Series A Preferred Stock for each share of Common Stock, at an exercise price of $150, subject to adjustment (the exercise price being referred to herein as the "Purchase Price"). The description and terms of the Rights are set forth in the Amended Rights Agreement.

The Rights will be evidenced, with respect to any certificate of Common Stock outstanding prior to the Distribution Date (as defined below), by that stock certificate and no separate certificates for the Rights will be issued. Prior to the Distribution Date, the Rights will only be transferable with the Common Stock, and a transfer of Common Stock will also constitute a transfer of the corresponding Rights.

Subject to limited exceptions, Genzyme will mail separate certificates for the Rights ("Right Certificates") upon the earlier of (i) the tenth day (or such later date as the Board of Directors of Genzyme (the "Board") may determine) following Genzyme's public announcement that a person or group has acquired 15% or more of the combined voting power of Genzyme's outstanding Common Stock (such person or group being hereinafter referred to as an "Acquiring Person") or (ii) the tenth business day (or such later date as the Board may determine) after any person or group commences, or announces an intention to commence, a tender or exchange offer which would, if completed, result in the offeror owning 15% or more of the combined voting power of Genzyme's outstanding Common Stock. The earlier of the dates described in (i) and (ii) above is called the "Distribution Date." The Rights cannot be exercised until the Distribution Date. Until a Right is exercised, holding a Right will not confer rights as a stockholder of Genzyme, such as the right to vote or to receive dividends. The Rights expire on March 28, 2009.

The Rights generally may be redeemed by action of the Board at $0.0005 per Right at any time prior to the tenth day following Genzyme's public announcement that a person has become an Acquiring Person.

Series A Preferred Stock purchasable upon exercise of the Rights will not be redeemable. Each share of Series A Preferred Stock will be entitled to a minimum preferential quarterly dividend payment of $1 per share, but will be entitled to an aggregate dividend of 200 times the dividend declared per share of Common Stock. Each share of Series A Preferred Stock will have 200 votes and will vote together with the Common Stock. In the event of any merger, consolidation or other transaction in which Common Stock is exchanged, each share of Series A Preferred Stock will be entitled to receive 200 times the amount received per share of Common Stock.

Because of the nature of the Series A Preferred Stock's dividend, liquidation and voting rights, the value of the one two-hundredth interest in a share of Series A Preferred Stock purchasable upon exercise of each Right should approximate the value of one share of Common Stock.

To preserve the economic value of the Rights, in the event of any stock dividends, stock splits, recapitalizations, reclassifications or other similar changes in capitalization, the number of shares of Series A Preferred Stock (or the number and kind of other securities) issuable upon exercise of each Right, the Purchase Price and redemption price in effect at such time (including the number of Rights or fractional Rights associated with each share of Common Stock) shall be adjusted as deemed appropriate by the Board. With certain exceptions, no adjustment in the Purchase Price will be required until cumulative adjustments require an adjustment of at least 1% in the Purchase Price. No fractional shares of Series A Preferred Stock will be issued (other than fractions which are integral multiples of one two-hundredth of a share of Series A Preferred Stock); instead, cash will be paid based on the then current market price of Series A Preferred Stock (as determined under the Amended Rights Agreement).

Upon an Acquiring Person becoming such, each holder of Rights, other than an Acquiring Person, will thereafter have the right to purchase a number of shares of Common Stock having a value equal to two times the exercise price of the corresponding Right. Genzyme also has the right, in such circumstances, to mandatorily exchange the Rights for shares of Common Stock.

Alternatively, if Genzyme is involved in a merger or other business combination in which Genzyme is not the surviving corporation at any time when any person owns 15% or more of the voting power of Genzyme's outstanding Common Stock, the Rights will entitle a holder (other than the 15% holder) to buy shares of common stock of the acquiring company having a market value of two times the Purchase Price of each Right.

Prior to the Distribution Date, the Board may amend any terms of the Rights without the consent of holders of certificates representing outstanding shares of Common Stock and Rights. From and after the Distribution Date, the Amended Rights Agreement may be amended without the approval of any holders of Rights only to (i) cure ambiguities, (ii) correct defective provisions, (iii) extend the redemption period for the rights, or (iv) change provisions as the Board deems necessary, but that will not adversely affect the interests of holders of the Rights. Under no circumstances, however, can the Amended Rights Agreement be amended to extend the redemption period after that period has expired.

The Rights have certain anti-takeover effects. The Rights can cause substantial dilution to a person or group that attempts to acquire Genzyme on terms that are not approved by the Board. The Rights should not interfere with any merger or other business combination that is approved by the Board because the Rights may be redeemed by Genzyme prior to the time that the Rights have become exercisable or the Amended Rights Agreement may be amended to exclude such transaction from its provisions.

The Amended Rights Agreement specifying the terms of the Rights and the Genzyme charter setting forth the terms of the Series A Preferred Stock are exhibits to this Registration Statement and are incorporated herein by reference. The foregoing description of the Rights is qualified in its entirety by reference to these exhibits.

Exhibit No.		Description
3.1		Restated Articles of Organization of Genzyme as filed with the Secretary of State of the Commonwealth of Massachusetts on May 28, 2004 (incorporated by reference to Exhibit 3.1 to Genzyme's Registration Statement on Form 8-A/A (File No. 0-14680), filed on May 28, 2004).
3.2		By-Laws of the Registrant (incorporated by reference to Exhibit 3.2 to the Genzyme's Quarterly Report on Form 10-Q for the quarter ended September 30, 1999 (File No. 0-14680)).
4.1		Fourth Amended and Restated Renewed Rights Agreement dated as of May 28, 2004 between the Registrant and American Stock Transfer & Trust Company. Filed herewith.

Pursuant to the requirements of Section 12 of the Securities Exchange Act of 1934, the registrant has duly caused this Amendment No. 3 to the registration statement to be signed on its behalf by the undersigned, thereunto duly authorized.

Date: May 27, 2004
	GENZYME CORPORATION
	By:	/s/ MICHAEL S. WYZGA Name: Michael S. Wyzga Title: Senior Vice President, Finance and Chief Financial Officer