Dear Chris, Love Henri

November 8, 2010

Mr. Christopher A. Viehbacher
Chief Executive Officer
Sanofi-Aventis
174, avenue de France
75635 Paris, Cedex 13

Dear Chris,

Since we last met, Genzyme has provided the marketplace with detailed reports on our significant progress and detailed information about our near-term plans and future prospects, including the results of an independent third party study of alemtuzumab's revenue potential. Sanofi-Aventis, for its own purposes, has chosen to dismiss or ignore this information and stick to its opportunistic and inadequate $69.00 per share offer, even as analysts have adjusted their targets to reflect the new information we have shared and we continue to have the support of our shareholders.

As we have repeatedly told Sanofi - and as our Lead Independent Director reaffirmed during our Investor Meeting -- our Board is unanimous in its view that the $69.00 offer is not an appropriate starting point for the discussions Sanofi seeks. Our shareholders understand and support this position. In addition, as our Board has also made clear, we are open to a transaction that appropriately recognizes Genzyme's intrinsic value and prospects. We will meet with Sanofi if it makes an offer that gives our Board of Directors reason to believe it will lead to that result.

Our Board is committed to taking all appropriate actions in the best interests of Genzyme and its shareholders and we have done, are doing, and will continue to do, exactly that.

Sincerely,

Henri A. Termeer
Chairman and Chief Executive Officer, Genzyme