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                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                   FORM 10-K/A
            [X] ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE
                         SECURITIES EXCHANGE ACT OF 1934
                   For the fiscal year ended December 31, 1998
                                       OR
          [ ] TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE
                         SECURITIES EXCHANGE ACT OF 1934

              For the transition period from _________ to ________
                         Commission File Number 0-21198

                                  ZONAGEN, INC.
             (Exact name of registrant as specified in its charter)

                     Delaware                                76-0233274
          (State of other jurisdiction of                 (I.R.S. Employer
          incorporation or organization)                 Identification No.)

         2408 Timberloch Place, Suite B-4         
               The Woodlands, Texas                             77380
     (Address of principal executive offices)                 (Zip Code)

       Registrant's telephone number, including area code: (281) 367-5892
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           Securities registered pursuant to Section 12(b) of the Act:

                Title of each class                     Name of each exchange on
                                                             which registered
                Common Stock, $.001 par value             Pacific Exchange, Inc.

           Securities registered pursuant to Section 12(g) of the Act:

                Title of each class                    Name of each exchange on
                                                            which registered
                Common Stock, $.001 par value           Nasdaq National Market

                Indicate by check mark whether the  Registrant (1) has filed all
reports  required to be filed by Section 13 or 15(d) of the Securities  Exchange
Act of 1934 during the preceding 12 months (or for such shorter  period that the
Registrant was required to file such reports),  and (2) has been subject to such
filing requirements for the past 90 days.
Yes /x/  No _____

                Indicate  by  checkmark  if  disclosure  of  delinquent  filings
pursuant to Item 405 of Regulation S-K is not contained herein,  and will not be
contained,  to the best of the  Registrant's  knowledge,  in definitive proxy or
information  statements  incorporated by reference in Part III of this Form 10-K
or any amendment to this Form 10-K. ______

                The  aggregate   market  value  of  the  voting  stock  held  by
non-affiliates of the registrant was approximately  $310,086,607 as of March 11,
1999, based on the closing sales price of the  registrant's  common stock on the
Nasdaq  National  Market on such date of $30.50 per share.  For  purposes of the
preceding sentence only, all directors, executive officers and beneficial owners
of ten  percent  or more of the  shares  of the  registrant's  common  stock are
assumed  to be  affiliates.  As of March  11,  1999,  11,220,894  shares  of the
registrant's common stock were outstanding.

                Certain sections of the registrant's  definitive proxy statement
relating to the registrant's  1999 annual meeting of  stockholders,  which proxy
statement  will be filed under the  Securities  Exchange  Act of 1934 within 120
days of the end of the  registrant's  fiscal year ended  December 31, 1998,  are
incorporated by reference into Part III of this Annual Report on Form 10-K.

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Explanation:

Registrant  is filing this 10-K/A  solely to properly  indicate on the cover the
"Securities Registered Pursuant to Section 12(g) of the Act."






                                   SIGNATURES

                Pursuant  to the  requirements  of  Section  13 or 15 (d) of the
Securities  Exchange Act of 1934,  the Registrant has duly caused this report to
be signed on its behalf by the undersigned, thereunto duly authorized on April
6, 1999.

                                               ZONAGEN, INC.


                                               By:  /s/ Joseph S. Podolski
                                                    ---------------------------
                                                    Joseph S. Podolski
                                                    President and Chief 
                                                      Executive Officer