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                                                                    EXHIBIT 31.1


                                 CERTIFICATIONS

I, Gilles Gagnon, President and Chief Executive Officer of AEterna Zentaris Inc.
(formerly named AEterna Laboratories Inc.), certify that:

     1.   I have reviewed this annual report on Form 40-F of AEterna Zentaris
          Inc. (formerly named AEterna Laboratories Inc.);

     2.   Based on my knowledge, this report does not contain any untrue
          statement of a material fact or omit to state a material fact
          necessary to make the statements made, in light of the circumstances
          under which such statements were made, not misleading with respect to
          the period covered by this report;

     3.   Based on my knowledge, the financial statements, and other financial
          information included in this report, fairly represent in all material
          respects the financial condition, results of operations and cash flows
          of the issuer as of, and for, the periods presented in this report;

     4.   The issuer's other certifying officer(s) and I are responsible for
          establishing and maintaining disclosure controls and procedures (as
          defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) for the issuer
          and have:

               a)   designed such disclosure controls and procedures, or caused
                    such disclosure controls and procedures to be designed under
                    our supervision, to ensure that material information
                    relating to the issuer, including its consolidated
                    subsidiaries, is made known to us by others within those
                    entities, particularly during the period in which this
                    report is being prepared;

               b)   [(omitted pursuant to the guidance of Release 33-8283
                    (June 5, 2003)]

               c)   evaluated the effectiveness of the issuer's disclosure
                    controls and procedures and presented in this report our
                    conclusions about the effectiveness of the disclosure
                    controls and procedures, as of the end of the period covered
                    by this report; and

               d)   disclosed in this report any change in the issuer's internal
                    control over financial reporting that occurred during the
                    period covered by the annual report that has materially
                    affected, or is reasonably likely to materially affect, the
                    issuer's internal control over financial reporting; and

     5.   The issuer's other certifying officer(s) and I have disclosed, based
          on our most recent evaluation of internal control over financial
          reporting, to the issuer's auditors and the Audit Committee of the
          issuer's Board of Directors (or persons performing the equivalent
          functions):

               a)   all significant deficiencies and material weaknesses in the
                    design or operation of internal control over financial
                    reporting which are reasonably likely to adversely


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                    affect the issuer's ability to record, process, summarize
                    and report financial information; and

               b)   any fraud, whether or not material, that involves management
                    or other employees who have a significant role in the
                    issuer's internal control over financial reporting.


Dated: October 22, 2004




/s/ Gilles Gagnon
-------------------------------------
Gilles Gagnon
President and Chief Executive Officer