<PAGE>

                     THE UNION LIGHT, HEAT AND POWER COMPANY

                                       AND

                                FIFTH THIRD BANK,
                                     Trustee

                                ----------------

                          Fourth Supplemental Indenture

                         Dated as of September 17, 1999

                                       To

                                    Indenture

                            Dated as of July 1, 1995

                                ----------------


                           7.875% Debentures Due 2009


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     FOURTH SUPPLEMENTAL INDENTURE, dated as of September 17, 1999, between The
Union Light, Heat and Power Company, a corporation duly organized and existing
under the laws of the Commonwealth of Kentucky (herein called the "Company"),
having its principal office at 139 East Fourth Street, Cincinnati, Ohio 45202,
and Fifth Third Bank, an Ohio banking corporation, as Trustee (herein called the
"Trustee") under the Indenture dated as of July 1, 1995 between the Company and
the Trustee (the "Indenture").

                             Recitals of the Company

     The Company has executed and delivered the Indenture to the Trustee to
provide for the issuance from time to time of its unsecured debentures, notes or
other evidences of indebtedness (the "Securities"), to be issued in one or more
series as in the Indenture provided.

     Pursuant to the terms of the Indenture, the Company desires to provide for
the establishment of a new series of its Securities to be known as its 7.875%
Debentures Due 2009 (herein called the "Debentures"), in this Fourth
Supplemental Indenture.

     All things necessary to make this Fourth Supplemental Indenture a valid
agreement of the Company have been done.

     Now, Therefore, This Fourth Supplemental Indenture Witnesseth:

     For and in consideration of the premises and the purchase of the Debentures
by the Holders thereof, it is mutually agreed, for the equal and proportionate
benefit of all Holders of the Debentures, as follows:


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                                  ARTICLE ONE

                             Terms of the Debentures

     Section 101. There is hereby authorized a series of Securities designated
the "7.875% Debentures Due 2009", limited in aggregate principal amount to
$20,000,000 (except as provided in Section 301(2) of the Indenture). The
Debentures shall mature and the principal shall be due and payable together with
all accrued and unpaid interest thereon on September 15, 2009 and shall be
issued in the form of a registered Global Security without coupons, registered
in the name of Cede & Co., as nominee of The Depository Trust Company (the
"Depositary").

     Section 102. The provisions of Section 305 of the Indenture applicable to
Global Securities shall apply to the Debentures.

     Section 103. Interest on each of the Debentures shall be payable
semiannually on March 15 and September 15 in each year (each an "Interest
Payment Date"), commencing on March 15, 2000, at the rate per annum specified in
the designation of the Debentures from September 17, 1999, or from the most
recent Interest Payment Date to which interest has been paid or duly provided
for. The interest so payable, and punctually paid or duly provided for, on any
Interest Payment Date will be paid to the Person in whose name such Debenture
(or one or more Predecessor Securities) is registered at the close of business
on the Regular Record Date for such interest, which shall be the Business Day
immediately preceding such Interest Payment Date. The amount of interest payable
for any period will be computed on the basis of a 360-day year of twelve 30-day
months. As used herein, "Business Day" means any day, other than a


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Saturday or Sunday, or a day on which banking institutions in New York, New
York are authorized or obligated by law or executive order to be closed.

     Section 104. Subject to agreements with or the rules of the Depositary or
any successor book-entry security system or similar system with respect to
Global Securities, payments of interest will be made by check mailed to the
Holder of each Debenture at the address shown in the Security Register, and
payments of the principal amount of each Debenture will be made at maturity by
check against presentation of the Debenture at the office or agency of the
Trustee.

     Section 105. The Debentures shall be issued in denominations of $1,000 or
any integral multiple of $1,000.

     Section 106. Principal and interest on the Debentures shall be payable in
the coin or currency of the United States of America, which, at the time of
payment, is legal tender for public and private debts.

     Section 107. The Debentures shall be subject to defeasance and covenant
defeasance, at the Company's option, as provided for in Sections 1302 and 1303
of the Indenture.

     Section 108. Subject to the terms of Article Eleven of the Indenture, the
Company shall have the right to redeem the Debentures, in whole but not in part,
from time to time and at any time (such redemption, an "Optional Redemption",
and the date thereof, the "Optional Redemption Date") upon not less than 30
days' notice to the holders, at a redemption price equal to the sum of (A) the
greater of (i) 100% of the principal amount of the Debentures to be redeemed or
(ii) the sum of the present values of the Remaining Scheduled Payments


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thereon discounted to the Optional Redemption Date on a semiannual basis
(assuming a 360-day year consisting of twelve 30-day months) at the Treasury
Rate plus 25 basis points, less the Applicable Accrued Interest Amount plus
(B) the Applicable Accrued Interest Amount.

     "Applicable Accrued Interest Amount" means, at the Optional Redemption
Date, the amount of interest accrued and unpaid from the prior interest payment
date to the Optional Redemption Date on the Debentures subject to the Optional
Redemption determined at the rate per annum shown in the title thereof, computed
on the basis of a 360-day year of twelve 30-day months.

     "Comparable Treasury Issue" means the United States Treasury security
selected by an Independent Investment Banker as having a maturity that would be
utilized, at the time of selection and in accordance with customary financial
practice, in pricing new issues of corporate debt securities of comparable
maturity to the remaining term of the Debentures to be redeemed pursuant to the
Optional Redemption. "Independent Investment Banker" means one of the Reference
Treasury Dealers appointed by the Trustee after consultation with the Company.

     "Comparable Treasury Price" means, with respect to the Optional Redemption
Date, the average of the Reference Treasury Dealer Quotations for such Optional
Redemption Date.

     "Reference Treasury Dealer" means a primary U.S. Government securities
dealer in New York City. "Reference Treasury Dealer Quotations" means, with
respect to each Reference Treasury Dealer and any redemption date, the average,
as determined by the Trustee, of the bid and asked prices for the Comparable


                                       Page 5
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Treasury Issue (expressed in each case as a percentage of its principal amount)
quoted in writing to the Trustee by such Reference Treasury Dealer at 5:00 p.m.
on the third Business Day preceding such redemption date.

     "Remaining Scheduled Payments" means, with respect to any Debenture, the
remaining scheduled payments of the principal thereof to be redeemed and
interest thereon that would be due after the Optional Redemption Date but for
the Optional Redemption.

     "Treasury Rate" means, with respect to the Optional Redemption Date (if
any), the rate per annum equal to the semiannual equivalent yield to maturity of
the Comparable Treasury Issue, assuming a price for the Comparable Treasury
Issue (expressed as a percentage of its principal amount) equal to the
Comparable Treasury Price for such Optional Redemption Date.

                                   ARTICLE TWO

                             Form of the Debentures

     Section 201. The Debentures are to be substantially in the following form
and shall include substantially the legend shown so long as the Debentures are
Global Securities:



                           (FORM OF FACE OF DEBENTURE)

No.  R-_                                                  $__________

CUSIP No.  906888 AP 7

                     THE UNION LIGHT, HEAT AND POWER COMPANY

                            7.875% DEBENTURE DUE 2009


                                       Page 6
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UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE
DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION ("DTC") TO ISSUER OR ITS AGENT
FOR REGISTRATION OF TRANSFER, EXCHANGE, OR PAYMENT AND ANY CERTIFICATE ISSUED IS
REGISTERED IN THE NAME OF CEDE & CO. OR IN SUCH OTHER NAME AS IS REQUESTED BY AN
AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE TO CEDE & CO. OR TO
SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY
TRANSFER, PLEDGE, OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON
IS WRONGFUL INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST
HEREIN.

     THE UNION LIGHT, HEAT AND POWER COMPANY, a corporation duly organized and
existing under the laws of the Commonwealth of Kentucky (herein called the
"Company", which term includes any successor Person under the Indenture
hereafter referred to), for value received, hereby promises to pay to CEDE &
CO., or registered assigns, the principal sum of ______________ and No/100
Dollars ($__________) on September 15, 2009, and to pay interest thereon from
September 17, 1999 or from the most recent Interest Payment Date to which
interest has been paid or duly provided for, semiannually on March 15 and
September 15 in each year, commencing March 15, 2000, at the rate of 7.875% per
annum, until the principal hereof is paid or made available for payment. The
amount of interest payable on any Interest Payment Date shall be computed on the
basis of a 360-day year of twelve 30-day months. The interest so payable, and
punctually paid or duly provided for, on any Interest Payment Date will, as
provided in the Indenture, be paid to the Person in whose name this Security (or
one or more Predecessor Securities) is registered at the close of business


                                       Page 7
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on the Regular Record Date for such interest, which shall be the Business Day
immediately preceding such Interest Payment Date. Any such interest not so
punctually paid or duly provided for will forthwith cease to be payable to
the Holder on such Regular Record Date and may either be paid to the Person
in whose name this Security (or one or more Predecessor Securities) is
registered at the close of business on a Special Record Date for the payment
of such Defaulted Interest to be fixed by the Trustee, notice whereof shall
be given to Holders of Securities of this series not less than 10 days prior
to such Special Record Date, or be paid at any time in any other lawful
manner not inconsistent with the requirements of any securities exchange on
which the Securities of this series may be listed, and upon such notice as
may be required by such exchange, all as more fully provided in the Indenture.

     Payment of the principal of (and premium, if any) and interest on this
Security will be made at the corporate trust office of the Trustee maintained
for that purpose in the City of Cincinnati, in such coin or currency of the
United States of America as at the time of payment is legal tender for payment
of public and private debts; provided, however, that at the option of the
Company payment of interest may be made by check mailed to the address of the
Person entitled thereto as such address shall appear in the Security Register.

     Any payment on this Security due on any day which is not a Business Day in
the City of New York need not be made on such day, but may be made on the next
succeeding Business Day with the same force and effect as if made on the due
date and no interest shall accrue for the period from and after such date,


                                       Page 8
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unless such payment is a payment at maturity or upon redemption, in which case
interest shall accrue thereon at the stated rate for such additional days.

     As used herein, "Business Day" means any day, other than a Saturday or
Sunday, or a day on which banking institutions in New York, New York are
authorized or obligated by law or executive order to be closed.

     Reference is hereby made to the further provisions of this Security set
forth on the reverse hereof, which further provisions shall for all purposes
have the same effect as if set forth at this place.

     Unless the certificate of authentication hereon has been executed by the
Trustee referred to on the reverse hereof by manual signature, this Security
shall not be entitled to any benefit under the Indenture or be valid or
obligatory for any purpose.

     In Witness Whereof, the Company has caused this instrument to be duly
executed.

                     THE UNION LIGHT, HEAT AND POWER COMPANY

                        By..............................


CERTIFICATE OF AUTHENTICATION

Dated:

     This is one of the Securities of the series designated therein referred to
in the within-mentioned Indenture.

                                FIFTH THIRD BANK,
                                   as Trustee


                                       Page 9
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                         By.............................
                              Authorized Signatory


                         (FORM OF REVERSE OF DEBENTURE)

This Security is one of a duly authorized issue of securities of the Company
(herein called the "Securities"), issued and to be issued in one or more series
under an Indenture, dated as of July 1, 1995 (as supplemented, herein called the
"Indenture", which term shall have the meaning assigned to it in such
instrument), between the Company and Fifth Third Bank, as Trustee (herein called
the "Trustee", which term includes any successor trustee under the Indenture),
and reference is hereby made to the Indenture for a statement of the respective
rights, limitations of rights, duties and immunities thereunder of the Company,
the Trustee and the Holders of the Securities and of the terms upon which the
Securities are, and are to be, authenticated and delivered. This Security is one
of the series designated on the face hereof, limited in aggregate principal
amount to $20,000,000.

The Securities of this series are subject to optional redemption, in whole but
not in part, from time to time and at any time (such redemption, an "Optional
Redemption", and the date thereof, the "Optional Redemption Date") upon not less
than 30 days' notice to the holders, at a redemption price equal to the sum of
(A) the greater of (i) 100% of the principal amount of the Securities of this
series to be redeemed or (ii) the sum of the present values of the Remaining
Scheduled Payments thereon discounted to the Optional Redemption Date on a
semiannual basis (assuming a 360-day year consisting of twelve 30-day months) at
the Treasury Rate plus 25 basis points, less the Applicable Accrued Interest


                                       Page 10
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Amount plus (B) the Applicable Accrued Interest Amount.

"Applicable Accrued Interest Amount" means, at the Optional Redemption Date, the
amount of interest accrued and unpaid from the prior interest payment date to
the Optional Redemption Date on the Securities of this series subject to the
Optional Redemption determined at the rate per annum shown in the title thereof,
computed on the basis of a 360-day year of twelve 30-day months.

"Comparable Treasury Issue" means the United States Treasury security selected
by an Independent Investment Banker as having a maturity that would be utilized,
at the time of selection and in accordance with customary financial practice, in
pricing new issues of corporate debt securities of comparable maturity to the
remaining term of the Securities of this series to be redeemed pursuant to the
Optional Redemption. "Independent Investment Banker" means one of the Reference
Treasury Dealers appointed by the Trustee after consultation with the Company.

"Comparable Treasury Price" means, with respect to the Optional Redemption Date,
the average of the Reference Treasury Dealer Quotations for such Optional
Redemption Date.

"Reference Treasury Dealer" means a primary U.S. Government securities dealer in
New York City. "Reference Treasury Dealer Quotations" means, with respect to
each Reference Treasury Dealer and any redemption date, the average, as
determined by the Trustee, of the bid and asked prices for the Comparable
Treasury Issue (expressed in each case as a percentage of its principal amount)
quoted in writing to the Trustee by such Reference Treasury Dealer at 5:00 p.m.
on the third Business Day preceding such redemption date.

"Remaining Scheduled Payments" means, with respect to any Securities


                                       Page 11
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of this series, the remaining scheduled payments of the principal thereof to
be redeemed and interest thereon that would be due after the Optional
Redemption Date but for the Optional Redemption.

"Treasury Rate" means, with respect to the Optional Redemption Date (if any),
the rate per annum equal to the semiannual equivalent yield to maturity of the
Comparable Treasury Issue, assuming a price for the Comparable Treasury Issue
(expressed as a percentage of its principal amount) equal to the Comparable
Treasury Price for such Optional Redemption Date.

The Indenture contains provisions for defeasance at any time of the entire
indebtedness of this Security or certain restrictive covenants and Events of
Default with respect to this Security upon compliance with certain conditions
set forth in the Indenture.

If an Event of Default with respect to Securities of this series shall occur and
be continuing, the principal of the Securities of this series may be declared
due and payable in the manner and with the effect provided in the Indenture.

The Indenture permits, with certain exceptions as therein provided, the
amendment thereof and the modification of the rights and obligations of the
Company and the rights of the Holders of the Securities of each series to be
affected under the Indenture at any time by the Company and the Trustee with the
consent of the Holders of a majority in principal amount of the Securities at
the time Outstanding of each series to be affected. The Indenture also contains
provisions permitting the Holders of a majority in principal amount of the
Securities of each series at the time Outstanding, on behalf of the Holders of


                                       Page 12
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all Securities of such series, to waive compliance by the Company with certain
provisions of the Indenture and certain past defaults under the Indenture and
their consequences. Any such consent or waiver by the Holder of this Security
shall be conclusive and binding upon such Holder and upon all future Holders of
this Security and of any Security issued upon the registration of transfer
hereof or in exchange herefor or in lieu hereof, whether or not notation of such
consent or waiver is made upon this Security.

As provided in and subject to the provisions of the Indenture, the Holder of
this Security shall not have the right to institute any proceeding with respect
to the Indenture or for the appointment of a receiver or trustee or for any
other remedy thereunder, unless such Holder shall have previously given the
Trustee written notice of a continuing Event of Default with respect to the
Securities of this series, the Holders of not less than 35% in principal amount
of the Securities of this series at the time Outstanding shall have made written
request to the Trustee to institute proceedings in respect of such Event of
Default as Trustee and offered the Trustee reasonably satisfactory indemnity,
and the Trustee shall not have received from the Holders of a majority in
principal amount of Securities of this series at the time Outstanding a
direction inconsistent with such request, and shall have failed to institute any
such proceeding, for 60 days after receipt of such notice, request and offer of
indemnity. The foregoing shall not apply to any suit instituted by the Holder of
this Security for the enforcement of any payment of principal hereof or any
premium or interest hereon on or after the respective due dates expressed
herein.


                                       Page 13
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No reference herein to the Indenture and no provision of this Security or of the
Indenture shall alter or impair the obligation of the Company, which is absolute
and unconditional, to pay the principal of and any premium and interest on this
Security at the times, place and rate, and in the coin or currency, herein
prescribed.

As provided in the Indenture and subject to certain limitations therein set
forth, the transfer of this Security is registrable in the Security Register,
upon surrender of this Security for registration of transfer at the office or
agency of the Company in any place where the principal of and any premium and
interest on this Security are payable, duly endorsed by, or accompanied by a
written instrument of transfer in form satisfactory to the Company and the
Security Registrar duly executed by, the Holder hereof or his attorney duly
authorized in writing, and thereupon one or more new Securities of this series
and of like tenor, of authorized denominations and for the same aggregate
principal amount, will be issued to the designated transferee or transferees.

The Securities of this series are issuable only in registered form without
coupons in denominations of $1,000 and any integral multiple thereof. As
provided in the Indenture and subject to certain limitations therein set forth,
Securities of this series are exchangeable for a like aggregate principal amount
of Securities of this series and of like tenor of a different authorized
denomination, as requested by the Holder surrendering the same.

No service charge shall be made for any such registration of transfer or
exchange, but the Company may require payment of a sum sufficient to cover any
tax or other governmental charge payable in connection therewith.


                                       Page 14
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Prior to due presentment of this Security for registration of transfer, the
Company, the Trustee and any agent of the Company or the Trustee may treat the
Person in whose name this Security is registered as the owner hereof for all
purposes, whether or not this Security be overdue, and neither the Company, the
Trustee nor any such agent shall be affected by notice to the contrary.

All terms used in this Security which are defined in the Indenture shall have
the meanings assigned to them in the Indenture.

                                  ARTICLE THREE

                          Original Issue of Debentures

     Section 301. Debentures in the aggregate principal amount of $20,000,000,
may, upon execution of this Fourth Supplemental Indenture, or from time to time
thereafter, be executed by the Company and delivered to the Trustee for
authentication, and the Trustee shall thereupon authenticate and deliver said
Debentures upon a Company Order without any further action by the Company.

                                  ARTICLE FOUR

                       Paying Agent and Security Registrar

     Section 401. Fifth Third Bank will be the Paying Agent and Security
Registrar for the Debentures.

                                  ARTICLE FIVE

                                Sundry Provisions

     Section 501. Except as otherwise expressly provided in this Fourth
Supplemental Indenture or in the form of Debenture or otherwise clearly required
by the context hereof or thereof, all terms used herein or in said


                                      Page 15
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form of Debenture that are defined in the Indenture shall have the several
meanings respectively assigned to them thereby except that terms defined in
both this Fourth Supplemental Indenture and the Indenture shall have the
meanings assigned to them herein.

     Section 502. The Indenture, as supplemented by this Fourth Supplemental
Indenture, is in all respects ratified and confirmed, and this Fourth
Supplemental Indenture shall be deemed part of the Indenture in the manner and
to the extent herein and therein provided.

                               ------------------

     This instrument may be executed in any number of counterparts, each of
which so executed shall be deemed to be an original, but all such counterparts
shall together constitute but one and the same instrument.

     In Witness Whereof, the parties hereto have caused this Fourth Supplemental
Indenture to be duly executed as of the date first above written.

                     THE UNION LIGHT, HEAT AND POWER COMPANY

                            BY /s/ WILLIAM L. SHEAFER
                               ------------------------------
                                    William L. Sheafer
                                    Vice President and
                                        Treasurer



                          FIFTH THIRD BANK, as Trustee

                              BY /s/ KERRY R. BYRNE
                                 --------------------------
                                       Kerry R. Byrne
                                       Vice President


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