April 12, 2004

Sanofi-Synthélabo Commences U.S. Offer for Aventis

Sanofi-Synthélabo announces that the registration statement filed with the United States Securities and Exchange Commission (“SEC”) in connection with its proposed acquisition of Aventis has been declared effective by the SEC and that Sanofi-Synthélabo has commenced its U.S. offer for Aventis on April 12, 2004.

The U.S. offer is open to holders of Aventis ordinary shares who are located in the United States and to all holders of Aventis American Depositary Shares wherever located.

In accordance with article 7 of the COB rule no. 2002-04, this document was transmitted to the “Autorité des marchés financiers” (AMF) before its publication.

Important Information: In connection with the proposed acquisition of Aventis, Sanofi-Synthelabo has filed a registration statement on Form F-4 (File no. 333-112314), including a final prospectus/offer to exchange, and will file additional documents with the United States Securities and Exchange Commission (SEC). Investors are urged to read the registration statement, including the final prospectus/offer to exchange, and any other relevant documents filed with the SEC, including all amendments, because they contain important information. Free copies of the registration statement, including the final prospectus/offer to exchange, as well as other relevant documents filed with the SEC, may be obtained at the SEC’s web site at www.sec.gov. The final prospectus/offer to exchange and other transaction-related documents may be obtained for free from MacKenzie Partners, Inc., the information agent for the U.S. offer, at the following address: 105, Madison Avenue, New York, New York 10016; telephone 1-(212) 929-5500 (call collect) or 1-(800) 322-2885 (toll-free call); e-mail proxy@mackenziepartners.com.

In France, holders of Aventis securities are requested, with respect to the offer, to refer to the prospectus (note d’information), which has been granted visa number 04-0090 by the Autorité des marchés financiers (“AMF”) and which is available on the website of the AMF (www.amf-france.org) and without cost from: BNP Paribas Securities Services, GIS-Emetteurs, Service Logistique, Les Collines de l’Arche, 75450 Paris Cedex 9.

The public offer to holders of Aventis ordinary shares located in Germany (the “German Offer”) is being made in accordance with applicable German law and pursuant to an offer document/sales prospectus, which is available free of charge at BNP Paribas Securities Services, Grüneburgweg 14, D-60322 Frankfurt am Main (Fax: 069 - 152 05 277) and on the website of the Company (www.sanofi-synthelabo.com). Any decision to tender Aventis ordinary shares in exchange for Sanofi-Synthélabo ordinary shares under the German Offer must be taken exclusively with regard to the terms and conditions of the German Offer, as well as with regard to the information included in the offer document/sales prospectus, including any amendments thereto, issued in Germany.

The French Offer, the U.S. Offer and the German Offer are being made on substantially the same terms and completion of these offers is subject to the same conditions. It is intended that the three offers will expire at the same time.

Investors and security holders may obtain a free copy of the Form 20-F filed with the SEC on April 2, 2004 and any other documents filed by Sanofi-Synthélabo with the SEC at www.sec.gov as well as of the Reference Document filed with the AMF on April 2, 2004 N° 04-0391 with the French Autorité des Marchés Financiers at www.amf-france.org or directly from Sanofi-Synthélabo on our web site at: www.sanofi-synthelabo.com.