<PAGE>
                                  UNITED STATES
                       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):
                               September 21, 1999





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




        Missouri                                                 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


<PAGE>


ITEM 5.    OTHER EVENTS

           Reference is made to "Liquidity and Capital  Resources" and "Electric
Industry Restructuring" under "Management's Discussion and Analysis of Financial
Condition and Results of Operations" and to Note 7 of the "Notes to Consolidated
Financial  Statements" of the  Registrant's  Form 10-Q for the quarterly  period
ended June 30, 1999 for  information  regarding the  Registrant's  commitment to
purchase eight new combustion  turbine  generators (CTs) for approximately  $435
million to be  operated by a proposed  new  unregulated  generating  subsidiary.
Recently,  the  Registrant  committed to acquiring  an  additional  ten CTs. The
Registrant  is now  planning to acquire a total of  eighteen  CTs which will add
over 1,800 megawatts to the  Registrant's  net peaking capacity and are expected
to cost approximately  $877 million.  CTs with a total capacity of 427 megawatts
(seven CTs) are planned to be installed  in 2000,  532  megawatts  (four CTs) in
2001,  515 megawatts  (five CTs) in 2002,  and 326 megawatts  (two CTs) in 2003.
Except for  approximately 45 megawatts (one CT), the new capacity is expected to
be operated by the Registrant's proposed new unregulated generating subsidiary.

SAFE HARBOR STATEMENT

Statements  made in this Form 8-K 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, the Registrant is providing
this cautionary  statement to identify important factors that could cause actual
results to differ materially from those  anticipated.  Factors include,  but are
not  limited to, the effects of  regulatory  actions;  changes in laws and other
governmental actions;  competition;  future market prices for fuel and purchased
power, electricity, and natural gas, including the use of financial instruments;
average rates for electricity in the Midwest;  business and economic conditions;
interest rates;  weather  conditions;  fuel prices and availability;  generation
plant  performance;  monetary and fiscal policies;  and 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/ Steven R. Sullivan
                                                  ------------------------
                                                       Steven R. Sullivan
                                                Vice President, General Counsel
                                                         and Secretary


Date:  September 21, 1999

<PAGE>
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UNITED STATES
                       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):
                               September 21, 1999

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

        Missouri                                                 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

           Reference is made to "Liquidity and Capital  Resources" and "Electric
Industry Restructuring" under "Management's Discussion and Analysis of Financial
Condition and Results of Operations" and to Note 7 of the "Notes to Consolidated
Financial  Statements" of the  Registrant's  Form 10-Q for the quarterly  period
ended June 30, 1999 for  information  regarding the  Registrant's  commitment to
purchase eight new combustion  turbine  generators (CTs) for approximately  $435
million to be  operated by a proposed  new  unregulated  generating  subsidiary.
Recently,  the  Registrant  committed to acquiring  an  additional  ten CTs. The
Registrant  is now  planning to acquire a total of  eighteen  CTs which will add
over 1,800 megawatts to the  Registrant's  net peaking capacity and are expected
to cost approximately  $877 million.  CTs with a total capacity of 427 megawatts
(seven CTs) are planned to be installed  in 2000,  532  megawatts  (four CTs) in
2001,  515 megawatts  (five CTs) in 2002,  and 326 megawatts  (two CTs) in 2003.
Except for  approximately 45 megawatts (one CT), the new capacity is expected to
be operated by the Registrant's proposed new unregulated generating subsidiary.

SAFE HARBOR STATEMENT

Statements  made in this Form 8-K 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, the Registrant is providing
this cautionary  statement to identify important factors that could cause actual
results to differ materially from those  anticipated.  Factors include,  but are
not  limited to, the effects of  regulatory  actions;  changes in laws and other
governmental actions;  competition;  future market prices for fuel and purchased
power, electricity, and natural gas, including the use of financial instruments;
average rates for electricity in the Midwest;  business and economic conditions;
interest rates;  weather  conditions;  fuel prices and availability;  generation
plant  performance;  monetary and fiscal policies;  and 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/ Steven R. Sullivan
                                                  ------------------------
                                                       Steven R. Sullivan
                                                Vice President, General Counsel
                                                         and Secretary

Date:  September 21, 1999