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 is a presentation delivered at a town hall meeting held by Genzyme Corporation (“Genzyme”) for Genzyme employees on February 16, 2011, in connection with the Agreement and Plan of Merger, dated as of February 16, 2011, among sanofi-aventis, GC Merger Corp. and Genzyme.

Sanofi-aventis

Town hall meeting

February 16

th

, 2011

Forward-Looking 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; investors and security holders can obtain

free copies of these documents from 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.

Forward-Looking Statements

Any statements made in this communication that are not statements of historical fact, including statements about sanofi-aventis' beliefs and

expectations and statements about the acquisition of Genzyme, are forward-looking statements and should be evaluated as such.  Forward-

looking statements include statements that may relate to sanofi-aventis' plans, objectives, strategies, goals, future events, future revenues or

performance, and other information that is not historical information.  Factors that may materially affect such forward-looking statements include:

the risk that the acquisition of Genzyme may not be consummated for reasons including that the conditions precedent to the completion of the

acquisition may not be satisfied; the possibility that the expected benefits from the proposed transaction will not be realized, or will not be realized

within the anticipated time period; the risk that sanofi-aventis' and Genzyme's businesses will not be integrated successfully; the possibility of

disruption from the acquisition making it more difficult to maintain business and operational relationships; any actions taken by either of the

companies, including but not limited to, restructuring or strategic initiatives (including capital investments or asset acquisitions or dispositions). 

Sanofi-aventis does not undertake, and specifically disclaims, any obligation or responsibility to update or amend any of the information above

except as otherwise required by law.

Worldwide presence

(1) US + Canada + Porto Rico

(2) Western Europe + Eastern Europe + Turkey

(3) Australia + New Zealand

All results based on Press Release Feb 9th 2011

North America

15 106

employees

9, 484M€

(1)

Europe

54 815

employees

11,609M€

(2)

Japan

3 153 employees

2,225M€

Africa/Middle East

4 529 employees

Africa:

846M€

Middle East:

789M€

Latin America

8 891 employees

2,735M€

Asia-Pacific

15 081 employees

Asia:

1,983M€

Pacific

(3)

:

713M€

30,384

Sanofi-aventis -

A world leader

€

30,384 m

2010 NET SALES-GROSS OF 3,7%

COMPARED WITH 2009

ON A REPORTED BASIS

100,000

More than

100,000

EMPLOYEES WORLDWIDE

1

ONE

OF THE LARGEST

PHARMACEUTICAL

GROUPS IN THE WORLD

Achieving our ambition through core growth platforms

Growth platforms

Diabetes

Vaccines

Emerging Markets

Consumer Health Care

Innovative Products

Animal Health

-

A global sustainable healthcare partner focused on patients’

needs

-

Recognised

for our ability to transform scientific innovation into

hope and solutions for patients

Diabetes

Oncology

Cardiovascular

Atrial Fibrillation

Vaccines

Consumer

Heath Care

Our response to health issues

Our culture

CONFIDENCE

INNOVATION

RESPECT

SOLIDARITY

INTEGRITY

Town hall meeting

February 16

th

, 2011

General principles for working together

Acknowledge and recognize your unique know-how and build on your DNA

Genzyme brand

Greater Boston Area

Listen to you, understand your business and create a collaborative spirit to

take this forward together

Focus on the day-to-day business and continue to address priorities

especially re-supply to patients

Cross-functional dedicated teams with members from both companies will

drive pre-integration process

Manage in full respect to people and values, and ensure regular

communication

Organization for integration

•

Chris Viehbacher (co-chair)

•

Belén

Garijo (Integration Leader)

•

Jérôme

Contamine (Finance)

•

Karen Linehan (Legal)

•

Roberto Pucci (HR)

•

Laure Thibaud (Comm.)

•

Philippe

Luscan

(IA)

adhoc

•

Elias Zerhouni (R&D)

adhoc

•

Sanofi-aventis and Genzyme representation to

be defined by work stream

•

Integration Project Leader

•

Henri Termeer

(co-chair)

•

David Meeker (COO)

•

Michael S. Wyzga

(Finance)

•

Tom DesRosier

(Legal)

•

Zoltan

Csimma

(HR)

•

Caren Arnstein (Comm.)

•

Scott Canute (IA)

adhoc

•

Alan E. Smith (R&D)

adhoc

Integration

Steering Committee

Integration

Coordination

Committee

Work streams

Manufacturing

Proposed high-level organization for integration

HR integration

support & talent

management

Internal/external

communication

Metrics

Process management /

guidelines

Finance

HR

Purchasing

Legal

IT

Real Estate

Quality

work streams (business assessment, strategy, integration model)

Communication

Integration Steering Committee

R&D

3

Operations

Support

Functions

1

2

4

Integration Coordination Committee

High-level calendar

Q1

Q2

Q3

Q4

Legal process

(tender offer,

CVR registration)

Feb

16

th

Merger

agreement

Transaction

closing / Day 1

Understanding

and planning

Business continuity and integration

Feb 16

th

Global Kick-off

pre-integration

Legal

process

Pre-integration

work

Integration

work

Steering

Committees

country level

kick off

Questions & answers