UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                                ----------------

                                   SCHEDULE TO
                               (AMENDMENT NO. 10)

           TENDER OFFER STATEMENT UNDER SECTION 14(d)(1) OR 13(e)(1)
                     OF THE SECURITIES EXCHANGE ACT OF 1934

                                     AVENTIS
                       (Name of Subject Company (Issuer))

                                SANOFI-SYNTHELABO
                        (Name of Filing Person (Offeror))
                                ----------------

                                ORDINARY SHARES,
                   NOMINAL VALUE (EURO)3.82 PER ORDINARY SHARE
                         (Title of Class of Securities)

                              ISIN No. FR0000130460
                      (CUSIP Number of Class of Securities)
                                ----------------

                           AMERICAN DEPOSITARY SHARES
                     (EACH REPRESENTING ONE ORDINARY SHARE)
                         (Title of Class of Securities)

                                    053561106
                      (CUSIP Number of Class of Securities)
                                ----------------

                                  JOHN SPINNATO
                  GENERAL COUNSEL, VICE PRESIDENT AND SECRETARY
                             SANOFI-SYNTHELABO INC.
                                 90 PARK AVENUE
                               NEW YORK, NY 10016
                              TEL : (212) 551-4000
            (Name, address and telephone number of person authorized
      to receive notices and communications on behalf of the filing person)

                                   COPIES TO:

         LAURENT COHEN-TANUGI                           DAVID A. KATZ, ESQ.
SENIOR VICE PRESIDENT AND GENERAL COUNSEL         WACHTELL, LIPTON, ROSEN & KATZ
          SANOFI-SYNTHELABO                             51 WEST 52ND STREET
        174 AVENUE DE FRANCE                         NEW YORK, NEW YORK 10019
         75013 PARIS, FRANCE                             (212) 403-1000
       TEL : + 33 1 53 77 40 00

|_|      Check the box if the filing relates solely to preliminary
         communications made before commencement of a tender offer.

Check the appropriate boxes below to designate any transactions to which
thisstatement relates:

|X|      Third party tender offer subject to Rule 14d-1

|_|      Issuer tender offer subject to Rule 13e-4

|_|      Going private transaction subject to Rule 13e-3

|_|      Amendment to Schedule 13D under Rule 13d-2

Check the following box if the filing is a final amendment reporting the results
of the tender offer: |_|





     Sanofi-Synthelabo, a French societe anonyme, amends and supplements its
Tender Offer Statement on Schedule TO, as amended (the "Schedule TO"), filed
initially with the United States Securities and Exchange Commission on April 12,
2004 in connection with Sanofi-Synthelabo's offer to acquire (1) all ordinary
shares, nominal value (euro)3.82 per share, of Aventis, a French societe
anonyme, that are held by holders who are located in the United States and (2)
all American Depositary Shares of Aventis (each an "Aventis ADS", and each
Aventis ADS representing one Aventis ordinary share), held by holders wherever
located, pursuant to the terms and subject to the conditions set forth in the
definitive Prospectus, dated April 9, 2004, and the definitive Prospectus
Supplement, dated May 27, 2004 (collectively, the "Prospectus"), and the related
amended ADS Letter of Transmittal and amended Form of Acceptance (collectively
with the Prospectus, and as amended and supplemented hereby, the "Revised U.S.
Offer"). This amendment constitutes Amendment No. 10 to the Schedule TO.
Capitalized terms not otherwise defined herein shall have the meanings ascribed
to them in the Schedule TO.

ITEM 12.  EXHIBITS

          ITEM 12 IS AMENDED AND SUPPLEMENTED TO INCLUDE THE FOLLOWING EXHIBITS:

                (a)(5)(xxx)     Press Release, dated August 12, 2004, announcing
                                the definitive results of Sanofi-Synthelabo's
                                offer for Aventis (incorporated herein by
                                reference to the filing made by
                                Sanofi-Synthelabo pursuant to Rule 425(a) on
                                August 12, 2004)





                                    SIGNATURE

     After due inquiry and to the best of my knowledge and belief, I certify
that the information set forth in this Schedule TO is true, complete and
correct.

                                          SANOFI-SYNTHELABO

August 12, 2004                            By:    /s/ Jean-Claude Leroy
                                             -----------------------------------
                                          Name:  Jean-Claude Leroy
                                          Title: Senior Vice President--Strategy





                                  EXHIBIT INDEX

 EXHIBIT
  NUMBER                           DESCRIPTION
  ------                           -----------

(a)(1)(i)         ADS Letter of Transmittal (Aventis ADSs)*

(a)(1)(ii)        Notice of Guaranteed Delivery (Aventis ADSs)*

(a)(1)(iii)       Letter to Brokers, Dealers, Commercial Banks, Trust Companies
                  and Other Nominees (Aventis ADSs)*

(a)(1)(iv)        Letter to Clients from Brokers, Dealers, Commercial Banks,
                  Trust Companies and other Nominees (Aventis ADSs)*

(a)(1)(v)         Guidelines for Certification of Taxpayer Indemnification
                  Number on Substitute Form W-9*

(a)(1)(vi)        Form of Acceptance for Aventis Ordinary Shares*

(a)(1)(vii)       Technical Notice to French Financial Intermediaries and U.S.
                  Custodians (Aventis ordinary shares)*

(a)(1)(viii)      Letter to Clients from Brokers, Dealers, Commercial Banks,
                  Trust Companies and other Nominees (Aventis ordinary shares)*

(a)(1)(ix)        ADS Letter of Transmittal (Aventis ADSs) (Revised U.S.
                  Offer)****

(a)(1)(x)         Notice of Guaranteed Delivery (Aventis ADSs) (Revised U.S.
                  Offer) ****

(a)(1)(xi)        Letter to Brokers, Dealers, Commercial Banks, Trust Companies
                  and Other Nominees (Aventis ADSs) (Revised U.S. Offer) ****

(a)(1)(xii)       Letter to Clients from Brokers, Dealers, Commercial Banks,
                  Trust Companies and other Nominees (Aventis ADSs) (Revised
                  U.S. Offer) ****

(a)(1)(xiii)      Form of Acceptance for Aventis Ordinary Shares (Revised U.S.
                  Offer) ****

(a)(1)(xiv)       Technical Notice to French Financial Intermediaries and U.S.
                  Custodians (Aventis ordinary shares) (Revised U.S. Offer) ****

(a)(1)(xv)        Letter to Clients from Brokers, Dealers, Commercial Banks,
                  Trust Companies and other Nominees (Aventis ordinary shares)
                  (Revised U.S. Offer) ****

(a)(2)            None

(a)(3)            Not applicable

(a)(4)            Prospectus, dated April 9, 2004 (incorporated herein by
                  reference to the filing made by Sanofi-Synthelabo pursuant to
                  Rule 424(b)(5) on April 12, 2004 (File no: 333-112314))

(a)(4)(ii)        Preliminary Prospectus Supplement, dated May 4, 2004
                  (incorporated herein by reference to Post-Effective Amendment
                  No. 1 to Sanofi-Synthelabo's Registration Statement on Form
                  F-4, dated May 5, 2004 (File no: 333-112314))

(a)(4)(iii)       Definitive Prospectus Supplement, dated May 27, 2004
                  (incorporated herein by reference to the filing made by
                  Sanofi-Synthelabo pursuant to Rule 424(b)(5) on May 28, 2004
                  (File no: 333-112314))

(a)(5)(i)         Press release announcing the offer for Aventis, dated January
                  26, 2004 (incorporated herein by reference to the filing made
                  by Sanofi-Synthelabo pursuant to Rule 425(a) on January 26,
                  2004)

(a)(5)(ii)        Press release announcing commencement of U.S. offer, dated
                  April 12, 2004 (incorporated herein by reference to the filing
                  made by Sanofi-Synthelabo pursuant to Rule 425(a) on April 12,
                  2004)

(a)(5)(iii)       Text of newspaper advertisement dated April 12, 2004 and
                  published in the Wall Street Journal*

(a)(5)(iv)        Press release announcing the entry into an agreement with
                  GlaxoSmithKline regarding the divestiture of Arixtra(R),
                  Fraxiparine(R) and related assets, dated April 13, 2004
                  (incorporated herein by reference to the filing made by
                  Sanofi-Synthelabo pursuant to Rule 425(a) on April 13, 2004)

(a)(5)(v)         Press release announcing the decision of Board of Directors of
                  Sanofi-Synthelabo to distribute an interim dividend, dated
                  April 15, 2004 (incorporated herein by reference to the filing
                  made by Sanofi-Synthelabo pursuant to Rule 425(a) on April 15,
                  2004)

(a)(5)(vi)        Complaint of Aventis, dated April 19, 2004, filed in the
                  United States District Court for the District





 EXHIBIT
  NUMBER                           DESCRIPTION
  ------                           -----------

                  of New Jersey**

(a)(5)(vii)       Press release announcing improved friendly offer, dated April
                  26, 2004 (incorporated herein by reference to
                  Sanofi-Synthelabo's Form 6-K furnished to the SEC on April 26,
                  2004)

(a)(5)(viii)      Presentation given by Mr. Jean-Francois Dehecq in Paris,
                  France at an Information Meeting announcing the improved
                  friendly offer (incorporated herein by reference to the filing
                  made by Sanofi-Synthelabo pursuant to Rule 425(a) on April 26,
                  2004)

(a)(5)(ix)        Press release announcing the European Commission's approval of
                  the proposed acquisition of Aventis by Sanofi-Synthelabo,
                  dated April 27, 2004 (incorporated herein by reference to the
                  filing made by Sanofi-Synthelabo pursuant to Rule 425(a) on
                  April 27, 2004)

(a)(5)(x)         Press release announcing the postponement of the general
                  meeting of Sanofi-Synthelabo shareholders, dated May 4, 2004
                  (incorporated herein by reference to the filing made by
                  Sanofi-Synthelabo pursuant to Rule 425(a) on May 4, 2004)

(a)(5)(xi)        Press release announcing issuance of request for additional
                  information by U.S. Federal Trade Commission, dated May 5,
                  2004 (incorporated herein by reference to the filing made by
                  Sanofi-Synthelabo pursuant to Rule 425(a) on May 5, 2004)

(a)(5)(xii)       Press release announcing rescheduling of general meeting of
                  Sanofi-Synthelabo shareholders for June 23, 2003, dated May
                  14, 2004 (incorporated herein by reference to the filing made
                  by Sanofi-Synthelabo pursuant to Rule 425(a) on May 14,
                  2004)

(a)(5)(xiii)      Press release announcing, among other things, nominees for
                  election as directors of Sanofi-Synthelabo, dated May 26, 2004
                  (incorporated herein by reference to the filing made by
                  Sanofi-Synthelabo pursuant to Rule 425(a) on May 26, 2004)

(a)(5)(xiv)       Press release announcing extension of U.S. offer to June 30,
                  2004, dated May 26, 2004, (incorporated herein by reference to
                  the filing made by Sanofi-Synthelabo pursuant to Rule 425(a)
                  on May 26, 2004)

(a)(5)(xv)        Text of newspaper advertisement dated May 28, 2004 and
                  published in the Wall Street Journal****

(a)(5)(xvi)       Press release confirming extension of U.S. offer until June
                  30, 2004, dated June 1, 2004 (incorporated herein by reference
                  to the filing made by Sanofi-Synthelabo pursuant to Rule
                  425(a) on June 1, 2004)

(a)(5)(xvii)      Press release regarding new indications for Arixtra(R), dated
                  June 4, 2004 (incorporated herein by reference to the filing
                  made by Sanofi-Synthelabo pursuant to Rule 425(a) on June 4,
                  2004)

(a)(5)(xviii)     Employee communication regarding the offers, published in "La
                  Lettre Bleue No. 2", dated June 7, 2004 (incorporated herein
                  by reference to the filing made by Sanofi-Synthelabo pursuant
                  to Rule 425(a) on June 7, 2004)

(a)(5)(xix)       Press release announcing adjusted offer consideration after
                  confirmation of Aventis dividend, dated June 14, 2004
                  (incorporated herein by reference to the filing made by
                  Sanofi-Synthelabo pursuant to Rule 425(a) on June 14, 2004)

(a)(5)(xx)        Press Release, dated June 21, 2004, announcing the draft
                  structure of SANOFI-AVENTIS Management Committee (incorporated
                  herein by reference to the filing made by Sanofi-Synthelabo
                  pursuant to Rule 425(a) on June 22, 2004)

(a)(5)(xxi)       Press Release, dated June 22, 2004, announcing the AMF's
                  decision to postpone the closing date of Sanofi-Synthelabo's
                  Offer for Aventis until July 30, 2004 (incorporated herein by
                  reference to the filing made by Sanofi-Synthelabo pursuant to
                  Rule 425(a) on June 22, 2004)

(a)(5)(xxii)      Press Release, dated June 23, 2004, confirming the extension
                  of the U.S. Offer, the French Offer and the German Offer
                  (incorporated herein by reference to the filing made by
                  Sanofi-Synthelabo pursuant to Rule 425(a) on June 23, 2004)

(a)(5)(xxiii)     Presentation given by Mr. Jean-Francois Dehecq and other
                  Sanofi-Synthelabo executives in Paris, France at Annual
                  General Meeting of Sanofi-Synthelabo shareholders on June 23,
                  2004 (incorporated herein by reference to the filing made by
                  Sanofi-Synthelabo pursuant to Rule 425(a) on June 23, 2004)





 EXHIBIT
  NUMBER                           DESCRIPTION
  ------                           -----------

(a)(5)(xxiv)      Press Release, dated June 24, 2004, announcing the results of
                  Annual General Meeting of Sanofi-Synthelabo shareholders
                  (incorporated herein by reference to the filing made by
                  Sanofi-Synthelabo pursuant to Rule 425(a) on June 24, 2004)

(a)(5)(xxv)       Press Release, dated June 25, 2004, announcing that
                  Sanofi-Synthelabo and Pfizer have concluded an agreement on
                  the divestment of Campto(R) (Irinotecan), conditional upon
                  completion of Sanofi-Synthelabo's offer for Aventis
                  (incorporated herein by reference to the filing made by
                  Sanofi-Synthelabo pursuant to Rule 425(a) on June 25, 2004)

(a)(5)(xxvi)      Press Release, dated July 15, 2004, announcing that the U.S.
                  Federal Trade Commission's Bureau of Competition and Economics
                  has completed its review of Sanofi-Synthelabo's proposed
                  acquisition of Aventis (incorporated herein by reference to
                  the filing made by Sanofi-Synthelabo pursuant to Rule 425(a)
                  on July 15, 2004)

(a)(5)(xxvii)     Press Release, dated July 21, 2004, announcing
                  Sanofi-Synthelabo's consolidated sales for the first half of
                  2004 (incorporated herein by reference to the filing made by
                  Sanofi-Synthelabo pursuant to Rule 425(a) on July 21, 2004)

(a)(5)(xxviii)    Press Release, dated July 29, 2004, announcing that the U.S.
                  Federal Trade Commission has accepted Sanofi-Synthelabo's
                  consent decree (incorporated herein by reference to the filing
                  made by Sanofi-Synthelabo pursuant to Rule 425(a) on July 29,
                  2004)

(a)(5)(xxix)      Press Release, dated July 31, 2004, announcing the expiration
                  of the tender period for Sanofi-Synthelabo's offer for Aventis
                  (incorporated herein by reference to the filing made by
                  Sanofi-Synthelabo pursuant to Rule 425(a) on August 2, 2004)

(a)(5)(xxx)       Press Release, dated August 9, 2004, announcing the
                  provisional results of Sanofi-Synthelabo's offer for Aventis
                  (incorporated herein by reference to the filing made by
                  Sanofi-Synthelabo pursuant to Rule 425(a) on August 9, 2004)

(a)(5)(xxxi)      Press Release, dated August 12, 2004, announcing the
                  definitive results of Sanofi-Synthelabo's offer for Aventis
                  (incorporated herein by reference to the filing made by
                  Sanofi-Synthelabo pursuant to Rule 425(a) on August 12, 2004)

(b)(1)            Credit Facility Agreement, dated 25 January 2004 (incorporated
                  herein by reference to Exhibit 10.4 to the Registration
                  Statement on Form F-4 filed by Sanofi-Synthelabo (File No.
                  333-112314))

(b)(2)            Credit Facility Agreement, dated 26 April 2004 (incorporated
                  herein by reference to Exhibit 10.5 of the Post-Effective
                  Amendment No. 1 to Sanofi-Synthelabo's Registration Statement
                  on Form F-4, dated May 5, 2004 (File no: 333-112314))

(d)(1)            Agreement, dated April 25, 2004, between Sanofi-Synthelabo and
                  Aventis***

(d)(2)            Letter from Mr. Jean-Francois Dehecq to Mr. Igor Landau
                  confirming certain severance and other employment-related
                  benefits of Mr. Landau***

(d)(3)            Amendment Agreement, dated May 19, 2004, amending Schedule 1
                  to the Agreement, dated April 25, 2004, between Aventis and
                  Sanofi-Synthelabo (incorporated herein by reference to Exhibit
                  99.1 to Sanofi-Synthelabo's Form 6-K, dated May 21, 2004
                  (File No. 001-31368))

(g)               None

(h)(1)            Opinion of Wachtell, Lipton, Rosen & Katz regarding certain
                  United States federal income tax matters (incorporated herein
                  by reference to Exhibit 8.1 to the Registration Statement on
                  Form F-4 filed by Sanofi-Synthelabo (File No. 333-112314))

(h)(2)            Opinion of Linklaters regarding certain French tax matters
                  (incorporated herein by reference to Exhibit 8.2 to the
                  Registration Statement on Form F-4 filed by Sanofi-Synthelabo
                  (File No. 333-112314))
-----------------
*      Previously filed on Schedule TO dated April 12, 2004.
**     Previously filed on Amendment No. 1 to the Schedule TO dated April 20,
       2004.
***    Previously filed on Amendment No. 2 to the Schedule TO dated April 26,
       2004.
****   Previously filed on Amendment No. 4 to the Schedule TO dated May 28,
       2004.