Filed by Sanofi-Synthélabo
Pursuant to Rule 165 and Rule 425(a) under the United States Securities Act of 1933,
as amended

Subject Company: Aventis
Commission File No. 001-10378
Date: May 10, 2004

     On May 10, 2004 Sanofi-Synthelabo first used the following materials, which are substantially similar to materials previously filed with the Commission on May 4, 2004, during roadshow presentations to Aventis and Sanofi-Synthelabo shareholders. Sanofi-Synthelabo intends to continue to use these materials during presentations to investors, in both English and French versions.

     In connection with the proposed acquisition of Aventis, Sanofi-Synthélabo has filed with the United States Securities and Exchange Commission (SEC), a registration statement on Form F-4 (File no: 333-112314), which includes a prospectus/offer to exchange and related exchange offer materials, to register the Sanofi-Synthélabo ordinary shares (including Sanofi-Synthélabo ordinary shares represented by Sanofi-Synthélabo ADSs) to be issued in exchange for Aventis ordinary shares held by holders located in the United States and for Aventis ADSs held by holders wherever located and has also filed with the SEC a Statement on Schedule TO. Investors and holders of Aventis securities are strongly advised to read the registration statement and the prospectus/offer to exchange, the related exchange offer materials and the Statement on Schedule TO, and any other relevant documents filed with the SEC, as well as any amendments and supplements (including any supplement relating to Sanofi-Synthélabo’s revised offer), because they contain important information. Investors and holders of Aventis securities may obtain free copies of the registration statement, the prospectus/offer to exchange and related exchange offer materials, and the Statement on Schedule TO, as well as other relevant documents filed with the SEC, at the SEC’s web site at www.sec.gov. The prospectus/offer to exchange and other transaction-related documents are being mailed to Aventis securityholders eligible to participate in the U.S. offer and additional copies 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 connection with its revised offer, Sanofi-Synthelabo intends to distribute a supplement to the prospectus/offer to exchnage as soon as practicable.

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Important Information
In connection with the proposed acquisition of Aventis, Sanofi-Synthélabo has filed with the United States Securities and Exchange Commission (SEC), a registration statement on Form F-4 (File no: 333-112314), which includes a prospectus/offer to exchange and related exchange offer materials, to register the Sanofi-Synthélabo ordinary shares (including Sanofi-Synthélabo ordinary shares represented by Sanofi-Synthélabo ADSs) to be issued in exchange for Aventis ordinary shares held by holders located in the United States and for Aventis ADSs held by holders wherever located and Sanofi-Synthélabo has also filed a Statement on Schedule TO with the SEC. Investors and holders of Aventis securities are strongly advised to read the registration statement and the prospectus/offer to exchange, the related exchange offer materials and the Statement on Schedule TO, and any other relevant documents filed with the SEC, as well as any amendments and supplements (including the supplement relating to the revised offers) to those documents, because they contain important information. Investors and holders of Aventis securities may obtain free copies of the registration statement, the prospectus/ offer to exchange and related exchange offer materials, and the Statement on Schedule TO, as well as other relevant documents filed with the SEC, at the SEC’s web site at www.sec.gov. The prospectus/offer to exchange and other transaction-related documents are being mailed to Aventis securityholders eligible to participate in the U.S. offer and additional copies 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 connection with the revised offers, Sanofi-Synthelabo intends to distribute a supplement to the prospectus/offer to exchange as soon as practicable. In France, holders of Aventis securities are requested, with respect to the offer, to refer to the prospectus supplement (note d’information complémentaire), which has been granted visa number 04-384 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 and to the recommendation statement (note d’information en réponse) of Aventis when it is available.

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 and supplements 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.

This press release does not constitute an offer to purchase or exchange or the solicitation of an offer to sell or exchange any securities of Aventis or an offer to sell or exchange or the solicitation of an offer to buy or exchange any securities of Sanofi-Synthélabo, nor shall there be any sale or exchange of securities in any jurisdiction (including the United States, Germany, Italy and Japan) in which such offer, solicitation or sale or exchange would be unlawful prior to the registration or qualification under the laws of such jurisdiction. The distribution of this communication may, in some countries, be restricted by law or regulation. Accordingly, persons who come into possession of this document should inform themselves of and observe these restrictions. The solicitation of offers to buy Sanofi-Synthélabo ordinary shares (including Sanofi-Synthélabo ordinary shares represented by Sanofi-Synthélabo ADSs) in the United States will only be made pursuant to a prospectus and related offer materials that Sanofi-Synthélabo expects to send to holders of Aventis securities. The Sanofi-Synthélabo ordinary shares (including Sanofi-Synthélabo ordinary shares represented by Sanofi-Synthélabo ADSs) may not be sold, nor may offers to buy be accepted, in the United States prior to the time the registration statement becomes effective. No offering of securities shall be made in the United States except by means of a prospectus meeting the requirements of Section 10 of the United States Securities Act of 1933, as amended.

Forward-Looking Statements This communication contains forward-looking information and statements about Sanofi-Synthélabo, Aventis and their combined businesses after completion of the proposed acquisition. 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” and similar expressions. Although Sanofi-Synthélabo’s management believes that the expectations reflected in such forward-looking statements are reasonable, investors and holders of Aventis securities 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-Synthélabo, 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 made by Sanofi-Synthélabo and Aventis, including those listed under “Cautionary Statement Concerning Forward-Looking Statements” and “Risk Factors” in the prospectus/offer to exchange included in the registration statement on Form F-4 that Sanofi-Synthélabo has filed with the SEC (File no: 333-112314). Sanofi-Synthélabo does not undertake any obligation to update any forward-looking information or statements. You may obtain a free copy of the registration statement and prospectus/offer to exchange and other public documents filed with the SEC in the manner described above. 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.

Explanatory Notes   Developed Sales. When we refer to “developed sales” of a product, we mean consolidated sales, excluding sales of products to our alliance partners, but including those that are made through our alliances and which are not included in our consolidated sales. These alliances are with Bristol-Myers Squibb on Plavix®/Iscover® (clopidogrel) and Aprovel®/Avapro®/Karvea® (irbesartan), with Fujisawa on Stilnox ®/Myslee® (zolpidem), and with Organon on Arixtra® (fondaparinux). Our alliance partners provide us with information regarding their sales in order to allow us to calculate developed sales. We believe that developed sales are useful measurement tool because they demonstrate trends in the overall presence of our products in the market. Comparable Sales. When we refer to the change in our sales on a “comparable” basis, we mean that we exclude the impact of exchange rate fluctuations and changes in Group structure (acquisitions and divestitures of entities and rights to products as well as change in the consolidation percentage for consolidated entities). For any two periods, we exclude the impact of exchange rates by recalculating sales for the earlier period on the basis of exchange rates used in the later period. We exclude the impact of acquisitions by including sales for a portion of the prior period equal to the portion of the current period during which we owned the entity or product rights based on sales information we receive from the party from whom we make the acquisition. Similarly, we exclude sales in the relevant portion of the prior period when we have sold an entity or rights to a product.