Sanofi-aventis Sends Letter to Genzyme Seeking Clarification on Potential Board Actions

PARIS, November 8, 2010 - Sanofi-aventis (EURONEXT: SAN and NYSE: SNY) announced today that it has
sent a letter to Genzyme Corporation (Nasdaq: GENZ) requesting that Genzyme
clarify its position on a number of potential Board actions raised in
Genzyme's Schedule 14D-9.

Sanofi-aventis' letter also notes that it is encouraged by Genzyme's
decision to "probe and evaluate alternatives" including contacting third
parties but observes that sanofi-aventis has not been contacted by Genzyme or
its advisors. Sanofi-aventis continues to remain interested in working with
Genzyme on a constructive basis and is committed to a mutually agreeable
transaction.

Below is the full text of the letter that was sent to Genzyme, which is
also being filed with the U.S. Securities and Exchange Commission.

November 8, 2010

    VIA EMAIL, TELECOPIER AND DHL
    Mr. Henri Termeer
    Chairman, President and Chief Executive Officer
    Genzyme Corporation
    500 Kendall Street
    Cambridge, Massachusetts 02147
    USA

Dear Henri,

Now that Genzyme's third-quarter earnings have been released, you have
had the opportunity to speak to shareholders regarding Genzyme's business and
prospects (including the detailed presentation to analysts and investors on
October 22) and the market has had a chance to digest and react to all of
this information, we would again like to request that you meet with us to
discuss our proposal to acquire Genzyme. We continue to believe that our
proposal is compelling for your shareholders and would provide them with
immediate and substantial value that reflects the potential of Genzyme's
business and pipeline.

You have publicly disclosed that Genzyme's Board has authorized
management and the company's advisors to "probe and evaluate alternatives"
for Genzyme and its assets, including contacting third parties. We were
encouraged to hear this, but to date, we have not been contacted or included
in this process. We are prepared to meet with you and, if you prefer, with
your advisors, at any time to discuss our respective views as to the
appropriate value of Genzyme's business and prospects and how to move this
transaction process forward in a cooperative manner. As you will recall, at
our meeting in September, I proposed several pathways to advance our
discussions, such as providing us with some limited due diligence regarding
manufacturing or arranging a meeting with your commercial team to discuss the
prospects for alemtuzumab. We remain ready and willing to participate in any
such meetings.

You have expressed publicly (and, we understand, directly during your
conversations with Genzyme shareholders) that you are committed to maximizing
shareholder returns and that you value shareholders' voices. However, we note
certain comments in your Schedule 14D-9 that appear to be inconsistent with
that objective.

First, you indicated that you believe that the Genzyme Board can, at any
time, opt to immediately stagger the terms of its members, extending the
terms of two-thirds of Genzyme's current directors for an additional one to
three years. This action would deprive shareholders of the opportunity to
elect the full Genzyme Board at the 2011 annual meeting of shareholders, a
right they expressly demanded. As you know, in 2006, holders of more than 85%
of the outstanding shares of Genzyme common stock voted to approve an
amendment to Genzyme's Articles of Organization to provide that all directors
would be elected annually. Given this, we do not believe that it would be
appropriate for the Genzyme Board to disenfranchise shareholders by
unilaterally staggering the terms of directors.

Second, you stated that the Genzyme Board retains the ability to adopt a
"poison pill". As you are well aware, if adopted, the poison pill would
prevent Sanofi-Aventis from acquiring Genzyme, regardless of your
shareholders' support for a transaction.

Third, you indicated that the Genzyme Board may wield the Massachusetts
anti-takeover statutes in a manner that would, as a practical matter, prevent
Sanofi-Aventis from acquiring Genzyme without the cooperation of Genzyme's
Board, notwithstanding your shareholders' support of a transaction.

We believe it would be inappropriate for the Board to take these
defensive actions. If we are unable to have a direct dialog with you, in all
fairness you should allow your shareholders the opportunity to decide for
themselves whether or not to accept our proposal.

Your shareholders should know with certainty that you will not interfere
with their right to benefit from our offer by taking any of the actions
described above. Therefore, we ask that you take action to make the
Massachusetts anti-takeover statute inapplicable to our offer and confirm
that Genzyme's 2011 annual meeting of shareholders, including the election of
all directors, will be held on schedule on the fourth Thursday of May (May
26, 2011), as provided in your Bylaws.

It remains our preference to work together with you to reach a mutually
agreeable transaction. We continue to believe that a transaction is in the
best interests of the shareholders of both Genzyme and Sanofi-Aventis, and we
look forward to hearing from you.

Yours sincerely,

Sanofi-Aventis

    By : /s/ Christopher A. Viehbacher
    Christopher A. Viehbacher
    Chief Executive Officer
    cc: Genzyme Board of Directors

About sanofi-aventis

Sanofi-aventis, a leading global pharmaceutical company, discovers,
develops and distributes therapeutic solutions to improve the lives of
everyone. Sanofi-aventis is listed in Paris (EURONEXT: SAN) and in New York
(NYSE: SNY).

Important Additional Information

This communication is neither an offer to purchase nor a solicitation of
an offer to sell any securities. In connection with the proposed transaction,
sanofi-aventis and GC Merger Corp. have filed tender offer documents with the
U.S. Securities and Exchange Commission (the "SEC"). These documents have
been 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. The tender offer materials may 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, and may also be obtained at no charge at the website maintained by
the SEC at www.sec.gov.

Any statements made in this communication that are not statements of
historical fact, including statements about sanofi-aventis' beliefs and
expectations and statements about sanofi-aventis' proposed 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: sanofi-aventis' ability to successfully complete the
tender offer for Genzyme's shares or realize the anticipated benefits of the
transaction; delays in obtaining any approvals required for the transaction,
or an inability to obtain them on the terms proposed or on the anticipated
schedule; and the failure of any of the conditions to sanofi-aventis' tender
offer to be satisfied. Any information regarding Genzyme contained herein has
been taken from, or is based upon, publicly available information. Although
sanofi-aventis does not have any information that would indicate that any
information contained herein is inaccurate or incomplete, sanofi-aventis has
not had the opportunity to verify any such information and does not undertake
any responsibility for the accuracy or completeness of such information.
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.

Sanofi-aventis www.sanofi-aventis.com

Media Relations: +33-1-53-77-44-50, MR at sanofi-aventis.com, or Investor Relations: +33-1-53-77-45-45, IR at sanofi-aventis.com