Exhibit 31.1
                                                                    Page 1 of 2

                     RULE 13a-14(a)/15d-14(a) CERTIFICATION
                    OF PRINCIPAL EXECUTIVE OFFICER OF AMEREN
                   CORPORATION (required by Section 302 of the
                           Sarbanes-Oxley Act of 2002)


     I, Gary L. Rainwater, certify that:

     1. I have reviewed this report on Form 10-Q for the quarterly  period ended
March 31, 2004 of Ameren Corporation;

     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 present in all material respects the
financial  condition,  results of operations and cash flows of the registrant as
of, and for, the periods presented in this report;

     4. The  registrant's  other  certifying  officer 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 registrant 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
               registrant,  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)     Evaluated  the  effectiveness  of  the  registrant'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 based on such evaluation; and

        c)     Disclosed in this report any change in the registrant's  internal
               control  over  financial   reporting  that  occurred  during  the
               registrant's most recent fiscal quarter (the registrant's  fourth
               fiscal  quarter  in  the  case  of an  annual  report)  that  has
               materially  affected,  or  is  reasonably  likely  to  materially
               affect,   the   registrant's   internal  control  over  financial
               reporting; and

     5. The registrant's other certifying officer and I have disclosed, based on
our most recent evaluation of internal control over financial reporting,  to the
registrant's auditors and the audit committee of registrant'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  which are  reasonably
               likely to adversely  affect the  registrant's  ability to record,
               process, summarize and report financial information;  and

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                                                                    Exhibit 31.1
                                                                    Page 2 of 2



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



Date: May 10, 2004


                                            /s/ Gary L. Rainwater
                                            --------------------------------
                                            Gary L. Rainwater
                                            Chairman, President and
                                            Chief Executive Officer
                                            (Principal Executive Officer)