Filed by sanofi-aventis

Pursuant to Rule 425 under the Securities Act of 1933, as amended

Subject Company: Genzyme Corporation

Exchange Act Commission File No: 0-14680

The following investor presentation, entitled “Adding a New Global Platform to our Sustainable Growth Strategy” was made by sanofi-aventis and Genzyme Corporation (“Genzyme”) on February 16, 2011 to investors of the companies, in connection with the Agreement and Plan of Merger, dated as of February 16, 2011, among sanofi-aventis, GC Merger Corp., and Genzyme.

Adding a New Global Platform

to our Sustainable Growth Strategy

February 16, 2011

2

Forward Looking Statements

This presentation contains forward-looking statements as defined in the Private Securities Litigation Reform Act of 1995, as amended. Forward-looking

statements are statements that are not historical facts.  These statements include projections and estimates and their underlying assumptions, statements

regarding plans, objectives, intentions and expectations with respect to future financial results, events, operations, services, product development and

potential, and statements regarding future performance.  Forward-looking statements are generally identified by the words “expects,” “anticipates,”

“believes,” “intends,” “estimates,” “plans” and similar expressions.  Although sanofi-aventis’ management believes that the expectations reflected in such

forward-looking statements are reasonable, investors are cautioned that forward-looking information and statements are subject to various risks and

uncertainties, many of which are difficult to predict and generally beyond the control of sanofi-aventis, that could cause actual results and developments to

differ materially from those expressed in, or implied or projected by, the forward-looking information and statements.  These risks and uncertainties

include among other things, the uncertainties inherent in research and development, future clinical data and analysis, including post marketing, decisions

by regulatory authorities, such as the FDA or the EMA, regarding whether and when to approve any drug, device or biological application that may be filed

for any such product candidates as well as their decisions regarding labeling and other matters that could affect the availability or commercial potential of

such products candidates, the absence of guarantee that the products candidates if approved will be commercially successful, the future approval and

commercial success of therapeutic alternatives, the Group’s ability to benefit from external growth opportunities  as well as those discussed or identified in

the public filings with the SEC and the AMF made by sanofi-aventis, including those listed under “Risk Factors” and “Cautionary Statement Regarding

Forward-Looking Statements” in sanofi-aventis’ annual report on Form 20-F for the year ended December 31, 2009.  Other than as required by applicable

law, sanofi-aventis does not undertake any obligation to update or revise any forward-looking information or statements.

Important Information about this Transaction: This communication is neither an offer to purchase nor a solicitation of any offer to sell any securities.  In

connection with the proposed transaction, sanofi-aventis will file an amended tender offer statement and a registration statement on Form F-4 to register

certain securities and certain related documents and Genzyme will file a Solicitation/Recommendation Statement with respect to the exchange offer with

the U.S. Securities and Exchange Commission (the “SEC”). Genzyme shareholders are urged to read the registration statement and exchange offer

documents when they become available because they will contain important information that shareholders should consider before making any decision

regarding tendering their shares.  These documents will be mailed to all Genzyme shareholders of record.  These documents, as they may be amended from

time to time, contain important information about the proposed transaction and Genzyme shareholders are urged to read them carefully and in their

entirety before any decision is made with respect to the proposed transaction.  When available, documentation relating to the transaction may be obtained

at no charge at the website maintained by the SEC at www.sec.gov and may also be obtained at no charge by directing a request by mail to MacKenzie

Partners, Inc., 105 Madison Avenue, New York, New York 10016, or by calling toll-free at (800) 322-2885.  Free copies of the Solicitation/Recommendation

Statement will be made available by Genzyme by directing a request to Genzyme at 500 Kendall Street, Cambridge, MA 02142, Attention: Shareholder

Relations Department, or by calling 617-252-7500 and asking for the Shareholder Relations Department.

This communication shall not constitute an offer to sell or the solicitation of an offer to buy any securities, nor shall there be any sale of securities in any

jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. 

No offering of securities shall be made except by means of a prospectus meeting the requirements of the U.S. Securities Act of 1933, as amended, or an

exemption therefrom.

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Conference Call Speakers

sanofi-aventis

Christopher A. Viehbacher

Chief Executive Officer

Jérôme Contamine

Executive Vice President, Chief Financial Officer

Genzyme

Henri A. Termeer

Chairman of the Board, President, Chief Executive Officer

Rationale for sanofi-aventis

Christopher A. Viehbacher

Chief

Executive

Officer

5

A

Strategically Consistent and Financially Attractive

Acquisition for sanofi-aventis

Creates a meaningful new growth platform

Expands our footprint in biotechnology

Increases our U.S. presence

Bolts on to our existing business

Significantly contributes to our goal of sustainable earnings growth

Drives significant long-term value for our shareholders

Rationale for Genzyme

Henri A. Termeer

Chairman of the Board, President, CEO

7

The Right Transaction for Genzyme, its

Shareholders, and Other Stakeholders

Represents a new beginning for Genzyme

Tremendous value recognized by sanofi-aventis

in our record of innovation

in our unique and pioneering approach to serving patients

Shared exciting vision of the future in which Genzyme and sanofi-

aventis will grow and innovate

Genzyme to help sanofi-aventis to grow and to innovate

Sanofi-aventis believes in what we what we do, our people and our

potential 

Looking forward to building a sustainable future together

Transaction Overview

Jérôme Contamine

Executive Vice President, Chief

Financial Officer

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Sanofi-aventis to Acquire Genzyme

$74.00

per share in cash plus contingent value right (CVR)

Risk / reward on Lemtrada™

and sustained production of Cerezyme®

and Fabrazyme®

shared through CVR structure

CVR

security to be publicly traded

Transaction unanimously approved by both Boards of Directors

No financing conditions

Anti-trust clearance

already received in the U.S. and EU

Anticipated closing in early Q2 2011

10

CVR Structure

(1)

Production Milestone

Approval Milestone

Sales Milestone #1

Sales Milestone #2

Sales Milestone #3

Sales Milestone #4

Cash Payments

$1.00

per CVR

$1.00

per CVR

$2.00

per CVR

$3.00

per CVR

$4.00

per CVR

$3.00

per CVR

Triggers

Paid if specified

Cerezyme®

/

Fabrazyme®

production levels are

met in 2011

Paid upon final

FDA approval

of Lemtrada™

for

multiple sclerosis

(MS) indication

Paid if Lemtrada™

net sales post launch

exceed an aggregate

of

$400m

within four specified

quarters per territory

Paid if and when

Lemtrada™

global

net sales exceed

$1,800m

Paid if and when

Lemtrada™

global

net  sales exceed

$2,300m

Paid if and when

Lemtrada™

global

net

sales exceed

$2,800m

Estimated

Timing of

Potential

Payments

Jan 2012

~H2 2012

~2014

2014-2020

2015-2020

2016-2020

Upside

potential

if Lemtrada™

is

approved

for Multiple Sclerosis

to be

shared

between

Genzyme

and sanofi-aventis

shareholders

at

all levels

of sales performance

The CVR will

be

publicly

traded

on NASDAQ

(1)

Details are defined in the Merger Agreement and CVR Agreement to be filed with the SEC

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Genzyme Acquisition Delivers Significant Financial

Benefits

Revenue growth acceleration

Genzyme

to

benefit

from

sanofi-aventis’

extensive

resources

and

experience in manufacturing

Significant Business EPS accretion expected:

Accretive in Year 1 after closing

Accretion of €0.75

to €1.00

by 2013

(1)

Value-creating transaction:

Return on capital in excess of WACC expected by Year 2

Financial strength and flexibility maintained:

No change to sanofi-aventis

dividend policy

Strong free cash flow generated by combination

Strong investment grade credit ratings maintained

(1)

At exchange rate of €1 = $1.30

12

Transaction valued at $20.1bn, excluding CVR component

Net

cash

position

of

Genzyme:

~$800m

by

end

of

2010

Fully financed upfront cash transaction

Bridge

facilities

($10bn

to

be

refinanced

by

bond

issuance

and

$5bn

to be refinanced by cash flow)

Cash and/or issuance of commercial paper

Attractive cost of debt: 2.5% to 3%

Additional existing syndicated revolving credit facilities (€13bn)

Sanofi-aventis

Has Already Secured Acquisition

Financing

Next Steps

Christopher A. Viehbacher

Chief

Executive

Officer

14

A Clear Path Forward given Antitrust Clearance

already Granted in the U.S. and EU

Q1

Q2

Q3

Legal process

Tender offer, CVR registration

Feb 16

Merger

announcement

Early Q2

Anticipated

closing

Planning

Integration

Mid Feb

Kick-off

Legal

process

Pre-integration

process

Integration

process

Day 1

2011

Q&A