SECURITIES AND EXCHANGE COMMISSION
                              WASHINGTON, DC 20549



                                    FORM 8-K


                                 CURRENT REPORT




     Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934



                Date of Report (Date of earliest event reported):
                                  May 28, 2002





                               AMEREN CORPORATION
             (Exact name of registrant as specified in its charter)




        Missouri                         1-14756               43-1723446
(State or other jurisdiction           (Commission          (I.R.S. Employer
      of incorporation)                File Number)         Identification No.)




                 1901 Chouteau Avenue, St. Louis, Missouri 63103
              (Address of principal executive offices and Zip Code)






       Registrant's telephone number, including area code: (314) 621-3222




ITEM 5.   OTHER EVENTS AND REGULATION FD DISCLOSURE

          Reference is made to Note 2 (Federal - Midwest ISO and  Alliance  RTO)
to the  "Notes  to  Consolidated  Financial  Statements  (unaudited)"  in Ameren
Corporation's  Form 10-Q for the  quarterly  period ended March 31, 2002,  for a
discussion of the Federal Energy Regulatory  Commission's  (FERC) April 25, 2002
order  requiring  the Alliance  companies,  including  our  subsidiaries,  Union
Electric  Company   (AmerenUE)  and  Central  Illinois  Public  Service  Company
(AmerenCIPS),  to select the regional  transmission  organization (RTO) in which
they will participate within thirty days of the order. On May 28, 2002, we filed
with the FERC indicating that we would return to the Midwest  Independent System
Operator (MISO),  although the exact nature of our participation  (whether as an
individual transmission owner or through an independent transmission company) is
subject to further  negotiations.  Until the tariffs and other material terms of
our  participation in the MISO are finalized and approved by the FERC, we cannot
predict the impact ongoing RTO  developments  will have on our future  financial
condition, results of operation or liquidity.


Safe Harbor Statement

Statements  made in this report,  which are not based on historical  facts,  are
"forward-looking"  and, accordingly,  involve risks and uncertainties that could
cause actual results to differ  materially from those  discussed.  Although such
"forward-looking"  statements  have  been  made in good  faith  and are based on
reasonable assumptions,  there is no assurance that the expected results will be
achieved.  These statements include (without limitation) statements as to future
expectations,  beliefs, plans, strategies,  objectives,  events,  conditions and
financial  performance.  In connection with the "Safe Harbor"  provisions of the
Private  Securities  Litigation  Reform  Act  of  1995,  we are  providing  this
cautionary  statement  to identify  important  factors  that could cause  actual
results to differ materially from those anticipated. The following factors could
cause results to differ materially from management  expectations as suggested by
such "forward-looking" statements:

          o    the  effects  of  regulatory   actions,   including   changes  in
               regulatory policy;
          o    the effects of  participation in a FERC-approved  RTO,  including
               activities associated with the MISO and the Alliance RTO; and
          o    legal and administrative proceedings.



                                    SIGNATURE

          Pursuant to the  requirements 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.

                                             AMEREN CORPORATION
                                              (Registrant)


                                             By   /s/ Martin J. Lyons
                                               ------------------------------
                                                      Martin J. Lyons
                                                         Controller
                                               (Principal Accounting Officer)


Date:  May 30, 2002


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