Sanofi-aventis and Regeneron Pharmaceuticals reaffirm development commitment

Paris, France – January 10, 2005 – Sanofi-aventis (EURONEXT: SAN and NYSE: SNY) announced today that, following a review of the Vascular Endothelial Growth Factor (VEGF) Trap program, they have reaffirmed their commitment to develop the VEGF Trap in oncology in collaboration with Regeneron Pharmaceuticals Inc. (Nasdaq: REGN). The companies will evaluate the VEGF Trap in a variety of cancer types, both in single-agent studies and in combination with chemotherapy. Sanofi-aventis also announced that Regeneron has earned a $25 million clinical development milestone payment.

“This is an exciting time for us as we continue to gather evidence on the potential of the VEGF Trap to block the formation of blood vessels that fuel the growth of cancerous tumors. All of us at Regeneron are looking forward to working with sanofi-aventis to accelerate the development of the VEGF Trap,” noted Leonard S. Schleifer, M.D., Ph.D., Regeneron’s President and Chief Executive Officer. “Sanofi-aventis is clearly committed to discovery, development, and commercialization of innovative products. Its expertise in oncology, driven by its commitment to the VEGF Trap, can provide a great resource for us in moving the program forward.” Marc Cluzel, M.D., Ph.D., Vice President, International Development, Sciences & Medical Affairs of sanofi-aventis added : “this is an important partnership for sanofi-aventis and we continue to believe that the blockage of VEGF is one of the most innovative approaches to targeted cancer therapy.” In addition, the companies have agreed that the exclusive right to develop and commercialize the VEGF Trap for eye diseases through local delivery systems reverts today to Regeneron. The collaboration will not currently pursue systemic delivery for eye disease. In connection with this agreement, sanofi-aventis will make a one-time payment to Regeneron of $25 million, of which 50% is repayable to sanofi-aventis following commercialization of the VEGF Trap. About Sanofi-aventis Sanofi-aventis is the world’s 3rd largest pharmaceutical company, ranking number 1 in Europe. Backed by a world-class R&D organization, Sanofi-aventis is developing leading positions in seven major therapeutic areas: cardiovascular disease, thrombosis, oncology, diabetes, central nervous system, internal medicine, vaccines. Sanofi-aventis is listed in Paris (EURONEXT : SAN) and in New York (NYSE : SNY). For Sanofi-aventis : This press release contains forward-looking statements as defined in the Private Securities Litigation Reform Act of 1995. Forward-looking statements are statements that are not historical facts. These statements include financial projections and estimates and their underlying assumptions, statements regarding plans, objectives and expectations with respect to future operations, products and services, and statements regarding future performance. Forward-looking statements are generally identified by the words “expect,” “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 those discussed or identified in the public filings with the SEC and the AMF made by Sanofi-aventis and Aventis, including those listed under “Forward-Looking Statements” and “Risk Factors” in sanofi-aventis’s annual report on Form 20-F for the year ended December 31, 2003 and those listed under “Cautionary Statement Regarding Forward-Looking Statements” and “Risk Factors” in Aventis’s annual report on Form 20-F for the year ended December 31, 2003. Other than as required by applicable law, sanofi-aventis does not undertake any obligation to update or revise any forward-looking information or statements. About Regeneron Regeneron is a biopharmaceutical company that discovers, develops, and intends to commercialize therapeutic medicines for the treatment of serious medical conditions. Regeneron has therapeutic candidates in clinical trials for the potential treatment of cancer and eye diseases, rheumatoid arthritis and other inflammatory conditions, asthma, and obesity and has preclinical programs in other diseases and disorders. Regeneron corporate headquarters are in Tarrytown, NY. For more information, please visit www.regn.com.