<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 24, 1998





                               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

In March 1998, Ameren Corporation (the Registrant) announced plans to reduce its
operating  expenses,  including  plans to eliminate  approximately  400 employee
positions by mid-1999  through a hiring  freeze and a targeted  separation  plan
(the Plan). (See the Registrant's Form 10-Q for the quarterly period ended March
31, 1998.) In July 1998, the Registrant offered separation packages to employees
whose  positions  are to be  eliminated.  In the  third  quarter  of  1998,  the
Registrant  will  record  a  one-time  charge of  $25 million (which will reduce
earnings  $15  million,  or  $.11 per  share)  representing  costs  incurred  to
implement the Plan.

The Registrant expects that the hiring freeze and targeted  separation plan will
reduce its  operating  expenses  by  approximately  $10-$15  million in 1998 and
$20-$25 million annually thereafter.

In July 1997,  the United States  Environmental  Protection  Agency (EPA) issued
final regulations  revising the National Ambient Air Quality Standards for ozone
and particulate  matter. At that time,  specific  emission control  requirements
were still  being  developed.  In  September  1998,  the EPA issued a final rule
pertaining  to  nitrogen  oxide  emissions,   which  will  require   significant
additional  reductions in emissions from coal-fired  boilers.  Both Missouri and
Illinois  (where all of the  Registrant's  coal-fired  power  plant  boilers are
located)  are  included  in the  area  targeted  for  nitrogen  oxide  emissions
reductions as part of the EPA's regional control program. Reduction requirements
in nitrogen oxide emissions from the Registrant's coal-fired boilers will exceed
75% from  1990  levels  by the year  2003.  Because  of the  magnitude  of these
additional  reductions,  the Registrant will be required to incur  significantly
higher capital costs to meet future  compliance  obligations  for its coal-fired
boilers  or  purchase  power  from  other  sources,  either of which  could have
significantly   higher  operating  expenses  associated  with  compliance.   The
significant  nitrogen oxide emissions  reductions already achieved on several of
the  Registrant's  coal-fired  power  plants  will help to  reduce  the costs of
compliance with this regulation.

It is not yet possible to determine  the exact  magnitude of the nitrogen  oxide
emission reductions required on the Registrant's power plants because each State
has up to one year to  develop  a plan to  comply  with the EPA  rule.  However,
preliminary  analysis  of the  regulations  indicate  that  selective  catalytic
reduction  technology  will be required for some of the  Registrant's  units, as
well as other additional controls.

The full  details  of these  requirements  are  under  study by the  Registrant.
Currently,  the Registrant estimates that its additional capital expenditures to
comply with these regulations could range from $250-$350 million over the period
from 1999 to 2002.  Associated  operations and  maintenance  expenditures  could
increase  $10-$15  million  annually,  beginning in 2003.  The  Registrant  will
explore  alternatives to comply with these new regulations in order to minimize,
to the extent possible,  its capital costs and operating expenses. At this time,
the  Registrant  is unable to predict the ultimate  impact of these  revised air
quality  standards on its future financial  condition,  results of operations or
liquidity.

Statements  made in this filing  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 "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 electricity; average
rates for electricity in the Midwest;  changes in future technologies;  business
and  economic  conditions;  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/ Warner L. Baxter
                                                       ------------------------
                                                         Warner L. Baxter
                                                 Vice President and Controller


Date:  October 8, 1998
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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 24, 1998

                               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

In March 1998, Ameren Corporation (the Registrant) announced plans to reduce its
operating  expenses,  including  plans to eliminate  approximately  400 employee
positions by mid-1999  through a hiring  freeze and a targeted  separation  plan
(the Plan). (See the Registrant's Form 10-Q for the quarterly period ended March
31, 1998.) In July 1998, the Registrant offered separation packages to employees
whose  positions  are to be  eliminated.  In the  third  quarter  of  1998,  the
Registrant  will  record  a  one-time  charge of  $25 million (which will reduce
earnings  $15  million,  or  $.11 per  share)  representing  costs  incurred  to
implement the Plan.

The Registrant expects that the hiring freeze and targeted  separation plan will
reduce its  operating  expenses  by  approximately  $10-$15  million in 1998 and
$20-$25 million annually thereafter.

In July 1997,  the United States  Environmental  Protection  Agency (EPA) issued
final regulations  revising the National Ambient Air Quality Standards for ozone
and particulate  matter. At that time,  specific  emission control  requirements
were still  being  developed.  In  September  1998,  the EPA issued a final rule
pertaining  to  nitrogen  oxide  emissions,   which  will  require   significant
additional  reductions in emissions from coal-fired  boilers.  Both Missouri and
Illinois  (where all of the  Registrant's  coal-fired  power  plant  boilers are
located)  are  included  in the  area  targeted  for  nitrogen  oxide  emissions
reductions as part of the EPA's regional control program. Reduction requirements
in nitrogen oxide emissions from the Registrant's coal-fired boilers will exceed
75% from  1990  levels  by the year  2003.  Because  of the  magnitude  of these
additional  reductions,  the Registrant will be required to incur  significantly
higher capital costs to meet future  compliance  obligations  for its coal-fired
boilers  or  purchase  power  from  other  sources,  either of which  could have
significantly   higher  operating  expenses  associated  with  compliance.   The
significant  nitrogen oxide emissions  reductions already achieved on several of
the  Registrant's  coal-fired  power  plants  will help to  reduce  the costs of
compliance with this regulation.

It is not yet possible to determine  the exact  magnitude of the nitrogen  oxide
emission reductions required on the Registrant's power plants because each State
has up to one year to  develop  a plan to  comply  with the EPA  rule.  However,
preliminary  analysis  of the  regulations  indicate  that  selective  catalytic
reduction  technology  will be required for some of the  Registrant's  units, as
well as other additional controls.

The full  details  of these  requirements  are  under  study by the  Registrant.
Currently,  the Registrant estimates that its additional capital expenditures to
comply with these regulations could range from $250-$350 million over the period
from 1999 to 2002.  Associated  operations and  maintenance  expenditures  could
increase  $10-$15  million  annually,  beginning in 2003.  The  Registrant  will
explore  alternatives to comply with these new regulations in order to minimize,
to the extent possible,  its capital costs and operating expenses. At this time,
the  Registrant  is unable to predict the ultimate  impact of these  revised air
quality  standards on its future financial  condition,  results of operations or
liquidity.

Statements  made in this filing  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 "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 electricity; average
rates for electricity in the Midwest;  changes in future technologies;  business
and  economic  conditions;  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/ Warner L. Baxter
                                                       ------------------------
                                                         Warner L. Baxter
                                                 Vice President and Controller

Date:  October 8, 1998