<PAGE>


                                                   APPROVED BY THE CINERGY CORP.
                                         BOARD OF DIRECTORS ON DECEMBER 10, 1999

              JANUARY 1, 2000 AMENDMENT TO THE CINERGY CORP. UNION
                             EMPLOYEES' 401(k) PLAN

         The Cinergy Corp. Union Employees' 401(k) Plan, as amended and restated
effective January 1, 1998, is hereby amended pursuant to Article 11 thereof.
Amendments with respect to the modification of Sections 3.1, 4.1, and 7.1 are
effective January 1, 2000.

(1)      EXPLANATION OF AMENDMENTS

         The purpose of the amendments is to provide for automatic or passive
enrollment in the Plan as of each new employee's employment date. Section 3.1 is
amended, effective January 1, 2000, by providing that each new employee is
automatically enrolled in the Plan as a participant on his/her employment date
as to before-tax contributions unless the employee notifies the Plan
administrator in writing that he/she declines participation.

         Section 4.1 is amended, effective January 1, 2000, to provide that each
new employee who is enrolled as a participant as of his/her employment date as
to before-tax contributions will be deemed to have made an initial deferred
percentage election of one percent.

         Section 7.1 is amended, effective January 1, 2000, to provide that the
automatic deferrals of new employees who are enrolled as participants as of
their employment dates as to before-tax contributions will be deposited in one
or more investment funds selected by the Plan Administrator and in accordance
with procedures established by the Plan Administrator.

(2)      AMENDMENTS EFFECTIVE JANUARY 1, 2000

         (a)      SECTION 3.1 AS AMENDED

                  Section 3.1, as hereby amended, reads as follows:

                  "3.1     PARTICIPATION.

                           Each Eligible Employee as of the Effective Date who
                           was a Participant in the Plan as of December 31, 1997
                           will continue to be a participant on the Effective
                           Date.

                           Prior to January 1, 2000, each other Eligible
                           Employee may commence participation in the Plan as of
                           the later of the Effective Date or the Eligible
                           Employee's Employment Commencement
<PAGE>

                           Date, by electing to make Employee After-Tax or
                           Deferred  Compensation Contributions, or by making a
                           Rollover Contribution, pursuant to Article 4
                           (Contributions).

                           On or after January 1, 2000, each other Eligible
                           Employee shall automatically commence participation
                           in the Plan as of the Eligible Employee's Employment
                           Commencement Date as to Employee Deferred
                           Compensation Contributions unless the Eligible
                           Employee affirmatively notifies the Plan
                           Administrator in writing that the Eligible Employee
                           does not desire to commence participation in the
                           Plan. Any Eligible Employee who affirmatively elects
                           not to participate in the Plan as of his Employment
                           Commence Date may subsequently commence participation
                           in the Plan by electing to make After-Tax or Deferred
                           Compensation Contributions, or by making a Rollover
                           Contribution, pursuant to Article 4 (Contributions).
                           Any Eligible Employee who commences participation as
                           of his Employment Commencement Date may also elect to
                           make Employee After-Tax Contributions or a Rollover
                           Contribution, pursuant to Article 4 (Contributions)."

         (b)      SECTION 4.1 AS AMENDED

                  Section 4.1, as hereby amended, reads as follows:

                  "4.1     DEFERRED COMPENSATION CONTRIBUTIONS

                            Each Participant may elect, in accordance with rules
                            established by the Plan Administrator, to reduce the
                            Participant's Compensation by any percentage up to
                            15 percent, in increments of one-half percent, and
                            to have the amount by which the Participant's
                            Compensation is reduced contributed on the
                            Participant's behalf by the Employer as a Deferred
                            Compensation Contribution to the Plan. Prior to
                            January 1, 2000, the election will be effective as
                            soon as administratively possible after the date the
                            Employee becomes eligible to participate and
                            notifies the Plan Administrator of the deferral
                            percentage. On or after January 1, 2000, each
                            Eligible Employee who becomes a Participant as of
                            his Employment Commencement Date will be deemed to
                            have made an initial deferral percentage election of
                            1 percent.

                            A participant may elect, in accordance with rules
                            established by the Plan Administrator, to increase,
                            decrease, or discontinue the Participant's
                            Compensation reductions. Such an election will be
                            effective as soon as administratively possible after
                            receipt of the election by the Plan Administrator
                            and will be effective only with respect to
                            Compensation not yet earned as of the effective date
                            of the election.

                            The Plan Administrator may adopt rules concerning
                            the administration of this section. The Deferred
                            Compensation Contributions made on behalf of each
                            Participant shall be paid by
<PAGE>

                            each Employer to the Trustee and allocated to the
                            Participant's Deferred Compensation Contributions
                            Account as soon as practical after the end of the
                            pay period to which the Deferred Compensation
                            Contributions relate, but in no case later than
                            the fifteenth business day of the month following
                            the month in which those amounts would otherwise
                            have been payable to the Participant."

         (c)      SECTION 7.1 AS AMENDED

                  Section 7.1, as hereby amended, reads as follows:

                  "7.1     AFTER-TAX, DEFERRED COMPENSATION, EMPLOYER MATCH,
                           ESOP TRANSFER, AND ROLLOVER CONTRIBUTION ACCOUNTS

                           (a)      INVESTMENT OF CONTRIBUTIONS. Each
                                    Participant may elect to have the After-Tax,
                                    Deferred Compensation, and Rollover
                                    Contributions made on the Participant's
                                    behalf invested in any one or more of the
                                    Investment Funds in increments of 1 percent,
                                    in accordance with procedures established by
                                    the Plan Administrator.

                           (b)      INVESTMENT TRANSFERS. Each Member may elect
                                    as of any date to have the assets in the
                                    Member's ESOP Transfer, Employer Match,
                                    After-Tax, Deferred Compensation, and
                                    Rollover Contributions Accounts reallocated
                                    among the Investment Funds, in increments of
                                    1 percent, in accordance with procedures
                                    established by the Plan Administrator.

                           (c)      INVESTMENT ELECTIONS. Each Participant may
                                    make the elections described in subsection
                                    (a) by making an election with the Plan
                                    Administrator upon becoming a Participant;
                                    PROVIDED, HOWEVER, that each Participant who
                                    (on or after January 1, 2000) commences
                                    participation as of his Employment
                                    Commencement Date will have his Deferred
                                    Compensation Contributions automatically
                                    deposited in one or more Investment Funds
                                    selected by the Plan Administrator and in
                                    accordance with procedures established by
                                    the Plan Administrator.

                           (d)      TRANSFER OF ASSETS. The Plan Administrator
                                    shall cause the transfer of moneys or other
                                    property from the appropriate Investment
                                    Fund to the other Investment Fund as may be
                                    necessary to carry out the aggregate
                                    transfer transactions elected by the
                                    Members, in accordance with uniform rules
                                    therefor established by the Plan
                                    Administrator."

         This Amendment is executed and approved by the duly authorized officers
         of Cinergy Corp., effective as of the dates set forth herein.

<PAGE>

                                            CINERGY CORP.


                                            By: ____________________________
                                                         James E. Rogers
                                                        Vice Chairman and
                                                     Chief Executive Officer


                                            Dated: _________________________


APPROVED:


By: _________________________________
           Jerome A. Vennemann
         Acting General Counsel
    and Assistant Corporate Secretary


Dated: ______________________________