<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):
                                January 11, 2001





                               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


<PAGE>


ITEM 5.         OTHER EVENTS AND REGULATION FD DISCLOSURE

Reference is made to Management's Discussion and Analysis of Financial Condition
and Results of Operations  under the caption  "Midwest ISO" and to Note 7 of the
Notes to Consolidated Financial Statements in the Registrant's Form 10-Q for the
quarterly  period ended September 30, 2000, for a discussion of the Registrant's
intention to withdraw from the Midwest Independent System Operator (MISO) and to
become a member of the Alliance  Regional  Transmission  Organization  (Alliance
RTO).

In  the  fourth  quarter  of  2000,  the  Registrant   recorded  a  $25  million
nonrecurring  charge ($15 million after income taxes, or 11 cents per share), as
a result of its  decision to  withdraw  from the MISO.  This  charge  relates to
Ameren's estimated obligation under the MISO agreement for costs incurred by the
MISO.

On January 11,  2001,  the  Registrant  signed an agreement to join the Alliance
RTO.  Regional   transmission   organizations,   including   independent  system
operators, are entities that ensure comparable and non-discriminatory  access to
regional electric transmission systems.  Following the announcements of Illinois
Power and Commonwealth Edison of their intent to withdraw from the MISO and join
the Alliance RTO, Ameren  determined that the operational  configuration  of the
MISO was  unacceptable  and  announced  its  withdrawal  in November  2000.  The
Registrant  decided to withdraw to ensure the  continued  reliable and efficient
operation of the Registrant's  transmission system. The Registrant's  withdrawal
from the MISO and its  membership  in the Alliance RTO are subject to regulatory
approvals.

Based on the  Registrant's  earnings results for the nine months ended September
30, 2000,  expected  higher fourth  quarter  sales,  and the  nonrecurring  MISO
charge,  the Registrant  estimates that reported earnings per share for the year
ended  December 31, 2000,  will range  between  $3.30 and $3.40.  On October 23,
2000, the Registrant had announced that it expected  reported earnings per share
for the year ended December 31, 2000,  would range between $3.25 and $3.35.  The
Registrant plans to announce its earnings for 2000 on February 6, 2001.

SAFE HARBOR STATEMENT

The foregoing estimates of the Registrant's  obligation under the MISO agreement
for costs incurred by the MISO and earnings for the year ended December 31, 2000
are  forward-looking   statements  within  the  meaning  of  the  "Safe  Harbor"
provisions  of the  Private  Securities  Litigation  Reform  Act of  1995.  Such
statements  involve risks and  uncertainties  that could cause actual results to
differ materially from those discussed herein. The following factors could cause
results to differ  materially from management  expectations as suggested by such
forward-looking statements: the effects of regulatory actions, including changes
in regulatory  policy;  changes in laws and other governmental  actions;  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;  wages and  employee  benefit  costs;  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/ Warner L. Baxter
                                                 ------------------------
                                                      Warner L. Baxter
                                                Vice President and Controller
                                                (Principal Accounting Officer)

Date:  January 12, 2001
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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):
                                January 11, 2001

                               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 Management's Discussion and Analysis of Financial Condition
and Results of Operations  under the caption  "Midwest ISO" and to Note 7 of the
Notes to Consolidated Financial Statements in the Registrant's Form 10-Q for the
quarterly  period ended September 30, 2000, for a discussion of the Registrant's
intention to withdraw from the Midwest Independent System Operator (MISO) and to
become a member of the Alliance  Regional  Transmission  Organization  (Alliance
RTO).

In  the  fourth  quarter  of  2000,  the  Registrant   recorded  a  $25  million
nonrecurring  charge ($15 million after income taxes, or 11 cents per share), as
a result of its  decision to  withdraw  from the MISO.  This  charge  relates to
Ameren's estimated obligation under the MISO agreement for costs incurred by the
MISO.

On January 11,  2001,  the  Registrant  signed an agreement to join the Alliance
RTO.  Regional   transmission   organizations,   including   independent  system
operators, are entities that ensure comparable and non-discriminatory  access to
regional electric transmission systems.  Following the announcements of Illinois
Power and Commonwealth Edison of their intent to withdraw from the MISO and join
the Alliance RTO, Ameren  determined that the operational  configuration  of the
MISO was  unacceptable  and  announced  its  withdrawal  in November  2000.  The
Registrant  decided to withdraw to ensure the  continued  reliable and efficient
operation of the Registrant's  transmission system. The Registrant's  withdrawal
from the MISO and its  membership  in the Alliance RTO are subject to regulatory
approvals.

Based on the  Registrant's  earnings results for the nine months ended September
30, 2000,  expected  higher fourth  quarter  sales,  and the  nonrecurring  MISO
charge,  the Registrant  estimates that reported earnings per share for the year
ended  December 31, 2000,  will range  between  $3.30 and $3.40.  On October 23,
2000, the Registrant had announced that it expected  reported earnings per share
for the year ended December 31, 2000,  would range between $3.25 and $3.35.  The
Registrant plans to announce its earnings for 2000 on February 6, 2001.

SAFE HARBOR STATEMENT

The foregoing estimates of the Registrant's  obligation under the MISO agreement
for costs incurred by the MISO and earnings for the year ended December 31, 2000
are  forward-looking   statements  within  the  meaning  of  the  "Safe  Harbor"
provisions  of the  Private  Securities  Litigation  Reform  Act of  1995.  Such
statements  involve risks and  uncertainties  that could cause actual results to
differ materially from those discussed herein. The following factors could cause
results to differ  materially from management  expectations as suggested by such
forward-looking statements: the effects of regulatory actions, including changes
in regulatory  policy;  changes in laws and other governmental  actions;  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;  wages and  employee  benefit  costs;  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/ Warner L. Baxter
                                                 ------------------------
                                                      Warner L. Baxter
                                                Vice President and Controller
                                                (Principal Accounting Officer)

Date:  January 12, 2001