<PAGE> 1


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

                      FIRST SUPPLEMENTAL INDENTURE


                                 between


                MERCANTILE BANCORPORATION INC., as Issuer,


                                  and


                  THE CHASE MANHATTAN BANK, as Trustee





                      Dated as of February 4, 1997

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



<PAGE> 2

                      TABLE OF CONTENTS

                          ARTICLE I
DEFINITIONS. . . . . . . . . . . . . . . . . . . . . . . . . . .2

                          ARTICLE II
GENERAL TERMS AND CONDITIONS OF THE DEBENTURES . . . . . . . . .4

                          ARTICLE III
REDEMPTION OF THE DEBENTURES. . . . . . . . . . . . . . . . . .10

                          ARTICLE IV
EXTENSION OF INTEREST PAYMENT PERIOD. . . . . . . . . . . . . .10

                          ARTICLE V
EXPENSES AND GUARANTEE. . . . . . . . . . . . . . . . . . . . .12

                          ARTICLE VI
FORM OF DEBENTURE . . . . . . . . . . . . . . . . . . . . . . .13

                          ARTICLE VII
MISCELLANEOUS . . . . . . . . . . . . . . . . . . . . . . . . .22


                                    i
<PAGE> 3

          FIRST SUPPLEMENTAL INDENTURE, dated as of February 4,
1997 (the "First Supplemental Indenture"), between Mercantile
Bancorporation Inc., a Missouri corporation (the "Company") and
The Chase Manhattan Bank, as trustee (the "Trustee"), under the
Indenture dated as of February 4, 1997 between the Company and
the Trustee (the "Indenture").

          WHEREAS, the Company executed and delivered the
Indenture to the Trustee to provide for the issuance of the
Company's unsecured junior subordinated debt securities to be
issued from time to time in one or more series as might be
determined by the Company under the Indenture, in an unlimited
aggregate principal amount which may be authenticated and
delivered as provided in the Indenture;

          WHEREAS, pursuant to the terms of the Indenture, the
Company desires to provide for the establishment of a series of
its Debt Securities to be known as Floating Rate Junior
Subordinated Deferrable Interest Debentures due 2027 (the
"Initial Debentures"), and to provide for, if and when issued in
exchange for the Initial Debentures pursuant to the Indenture and
the Registration Agreement, a series of its Debt Securities to be
known as Floating Rate Junior Subordinated  Deferrable Interest
Debentures due 2027 (the "Exchange Debentures" and together with
the Initial Debentures, the "Debentures"), the form and substance
of each such series of Debentures and the terms, provisions and
conditions thereof to be set forth as provided in the Indenture
and this First Supplemental Indenture;

          WHEREAS, Mercantile Capital Trust I, a Delaware
statutory business trust (the "Trust"), has offered for sale
pursuant to an exemption from the registration requirements of
the Securities Act of 1933, $150,000,000 aggregate liquidation
amount of Floating Rate Capital Trust Pass-through Securities
(the "Initial Capital Securities"), representing undivided
beneficial interests in the assets of the Trust and proposes to
invest the proceeds from such offering, together with the
proceeds of the issuance and sale by the Trust to the Company of
its common securities, in $154,640,000 aggregate principal amount
of the Debentures;

          WHEREAS, the Trust may offer and issue Floating Rate
Capital Trust Pass-through Securities (the "Exchange Capital
Securities") in exchange for the Initial Capital Securities; and

          WHEREAS, the Company has requested that the Trustee
execute and deliver this First Supplemental Indenture; all
requirements necessary to make this First Supplemental Indenture
a valid instrument in accordance with its terms, and to make the
Debentures, when executed by the Company and authenticated and
delivered by the Trustee, the valid obligations of the Company,
have been performed; and the execution and delivery of this First
Supplemental Indenture has been duly authorized in all respects;

          NOW THEREFORE, in consideration of the purchase and
acceptance of the Initial Debentures by the holders thereof, and
for the purpose of setting forth, as provided in the Indenture,
the form and substance of each series of Debentures and the
terms, provisions and conditions thereof, the Company covenants
and agrees with the Trustee as follows:



<PAGE> 4

                           ARTICLE I

                          DEFINITIONS

          SECTION 1.1
          -----------

          Unless the context otherwise requires:

          (a)  a term defined in the Indenture has the same
meaning when used in this First Supplemental Indenture;

          (b)  a term defined anywhere in this First Supplemental
Indenture has the same meaning throughout;

          (c)  the singular includes the plural and vice versa;

          (d)  a reference to a Section or Article is to a
Section or Article of this First Supplemental Indenture;

          (e)  headings are for convenience of reference only and
do not affect interpretation;

          (f)  the following terms have the meanings given to
them in the Declaration:  (i) Administrators; (ii) Business Day;
(iii) Capital Security Certificate; (iv) Capital Treatment Event;
(v) Clearing Agency; (vi) Delaware Trustee; (vii) Depositary;
(viii) Distribution; (ix) Institutional Trustee; (x) Purchase
Agreement; and (xi) Tax Event;

          (g)  the following terms have the meanings given to
them in this Section 1.1(g):

          "Additional Interest" shall have the meaning set forth
in Section 2.5(d).

          "Calculation Agent" means any Person authorized by the
Company to determine the interest rate of the Debentures, which
shall be The Chase Manhattan Bank, until a successor is
appointed.

          "Compounded Interest" shall have the meaning set forth
in Section 4.1.

          "Declaration" means the Amended and Restated
Declaration of Trust of the Trust, dated as of February 4, 1997,
as amended or supplemented from time to time.

          "Deferred Interest" shall have the meaning set forth in
Section 4.1.

          "Determination Date" means, with respect to any
interest period, the date that is two London Business Days prior
to the first day of such interest period.


                                    2
<PAGE> 5

          "Dissolution Event" means that, subject to the receipt
by the Company of prior approval from the Federal Reserve if then
required under applicable capital guidelines or policies of the
Federal Reserve, the Trust is to be dissolved in accordance with
the Declaration, and the Debentures held by the Institutional
Trustee are to be distributed to the holders of the Trust Securities
issued by the Trust pro rata in accordance with the Declaration.
                    --- ----

          "Extension Period" shall have the meaning set forth in
Section 4.1.

          "Federal Reserve" means the Board of Governors of the
Federal Reserve System.

          "Global Debenture" shall have the meaning set forth in
Section 2.4(a)(i).

          "interest" shall include all interest payable on a
series of Debentures including any Additional Interest,
Compounded Interest and Special Interest, if applicable.

          "LIBOR" means, with respect to a quarterly interest
period relating to an Interest Payment Date (in the following
order of priority):

          (i)   the rate (expressed as a percentage per annum) for
                Eurodollar deposits having a three-month maturity
                that appears on Telerate Page 3750 as of 11:00
                a.m. (London time) on the related Determination
                Date;

          (ii)  if such rate does not appear on Telerate Page 3750
                as of 11:00 a.m. (London time) on the related
                Determination Date, LIBOR will be the arithmetic
                mean (if necessary rounded upwards to the nearest
                whole multiple of .00001%) of the rates (expressed
                as percentages per annum) for Eurodollar deposits
                having a three-month maturity that appear on
                Reuters Monitor Money Rates Page LIBO ("Reuters
                Page LIBO") as of 11:00 a.m. (London time) on such
                Determination Date;

          (iii) if such rate does not appear on Reuters Page
                LIBO as of 11:00 a.m. (London time) on the related
                Determination Date, the Calculation Agent will
                request the principal London offices of four
                leading banks in the London interbank market to
                provide such banks offered quotations (expressed
                as percentages per annum) to prime banks in the
                London interbank market for Eurodollar deposits
                having a three-month maturity as of 11:00 a.m.
                (London time) on such Determination Date.  If at
                least two quotations are provided, LIBOR will be
                the arithmetic mean (if necessary rounded upwards
                to the nearest whole multiple of .00001%) of such
                quotations;

          (iv)  if fewer than two such quotations are provided as
                requested in clause (iii) above, the Calculation
                Agent will request four major New York City banks
                to provide such banks offered quotations
                (expressed as percentages per annum) to leading
                European banks for loans in Eurodollars as of
                11:00 a.m. (London time) on such Determination
                Date. If at least two such


                                    3
<PAGE> 6
                quotations are provided, LIBOR will be the arithmetic
                mean (if necessary rounded upwards to the nearest whole
                multiple of .00001%) of such quotations; and

          (v)   if fewer than two such quotations are provided as
                requested in clause (iv) above, LIBOR will be
                LIBOR determined with respect to the interest
                period immediately preceding such current interest
                period.

          If the rate for Eurodollar deposits having a three-
month maturity that initially appears on Telerate Page 3750 or
Reuters Page LIBO, as the case may be, as of 11:00 a.m. (London
time) on the related Determination Date is superseded on Telerate
Page 3750 or Reuters Page LIBO, as the case may be, by a
corrected rate before 12:00 noon (London time) on such
Determination Date, the corrected rate as so substituted on the
applicable page will be the applicable LIBOR for such
Determination Date.

          "London Business Day" means any day, other than a
Saturday or Sunday, on which banks are open for business in
London.

          "Maturity Date" means February 1, 2027.

          "Non-Book-Entry Capital Securities" shall have the
meaning set forth in Section 2.4(a)(ii).

          "Record Date" shall have the meaning set forth in the
Debentures.

          "Redemption Price" shall have the meaning set forth in
Section 3.1.

           "Registration Agreement" means the Registration Rights
Agreement, dated January 29, 1997, relating to the Debentures and
the other securities described therein among the Company, the
Trust and the initial purchasers named therein.

          "Registered Exchange Offer" has the meaning set forth
in the Registration Agreement.

          "Special Interest" has the meaning set forth in Section
2.5(f)(iii).

                          ARTICLE II

       GENERAL TERMS AND CONDITIONS OF THE DEBENTURES

          SECTION 2.1
          -----------

          The Initial Debentures and the Exchange Debentures are
hereby authorized as two series of Debt Securities. The
aggregate principal amount of Debentures outstanding at any time
shall not exceed $154,640,000 (except as set forth in Section
2.03(2) of the Indenture).  Upon receipt of a written order of
the Company for the authentication and delivery of a series of
Debentures and satisfaction of the requirements of Section 2.04
of the Indenture, the Trustee


                                    4
<PAGE> 7
shall authenticate (a) Initial Debentures for original issuance in an
aggregate principal amount not to exceed $154,640,000 (except as set
forth in Section 2.03(2) of the Indenture) or (b) Exchange Debentures
for issuance pursuant to a Registered Exchange Offer for Initial
Debentures in a principal amount equal to the principal amount of
Initial Debentures exchanged in such Registered Exchange Offer.

          The Initial Debentures shall be issued pursuant to an
exemption from registration under the Securities Act and the
Restricted Securities Legend shall appear thereon, unless
otherwise determined by the Company in accordance with applicable
law.  The Initial Debentures may not be transferred except in
compliance with the Restricted Securities Legend set forth in
Section 2.07 of the Indenture, unless otherwise determined by the
Company in accordance with applicable law.  The Initial
Debentures shall be issued in minimum denominations of $100,000
and any integral multiple of $1,000 in excess thereof, and the
Exchange Debentures shall be issuable in minimum denominations of
$1,000 and any integral multiple thereof.

          SECTION 2.2
          -----------

          At the Maturity Date, the Debentures shall mature and
the principal thereof shall be due and payable together with all
accrued and unpaid interest thereon including Compounded
Interest, Additional Interest and Special Interest thereon, if
any.

          SECTION 2.3
          -----------

          Except as provided in Section 2.4, Debentures of a
series shall be issued in fully registered certificated form
without interest coupons.  Principal and interest on Debentures
of a series issued in certificated form will be payable, the
transfer of such Debentures will be registrable and such
Debentures will be exchangeable for Debentures of such series
bearing identical terms and provisions at the office or agency of
the Company in the Borough of Manhattan, The City of New York,
which office or agency shall initially be the corporate trust
office of the Trustee; provided, however, that payment of
                       --------  -------
interest may be made at the option of the Company by check mailed
to the holder of any Debenture at such address as shall appear in
the Debt Security Register for such series of Debentures or by
wire transfer to an account appropriately designated by such
holder.  Notwithstanding the foregoing, so long as the holder of
any Debentures of a series is the Institutional Trustee, the
payment of the principal of and interest (including Compounded
Interest, Additional Interest and Special Interest, if any) on
the Debentures held by the Institutional Trustee will be made at
such place and to such account as may be designated by the
Institutional Trustee.

          SECTION 2.4
          -----------

          (a)  In connection with a Dissolution Event,

               (i)  except as provided in clause (ii) of this
     sentence, Debentures of a series in certificated form may be
     presented to the Trustee by the Institutional Trustee in
     exchange for a Global Security for such series in an
     aggregate principal amount equal to


                                    5
<PAGE> 8
     the aggregate principal amount of all outstanding Debentures of
     such series (a "Global Debenture"), to be registered in the name
     of The Depository Trust Company, New York, New York, or its
     nominee (hereby designated to be the Depositary for Debentures of
     such series), and delivered by the Trustee to the Depositary
     or its custodian for crediting to the accounts of the
     Depositarys participants pursuant to the instructions of
     the Administrators of the Trust, which instructions shall be
     provided in accordance with the terms of the Declaration;
     the Company upon any such presentation shall execute a
     Global Debenture for such series in such aggregate principal
     amount and deliver the same to the Trustee for authentication and
     delivery in accordance with the Indenture and this First
     Supplemental Indenture; payments on the Debentures of a series
     issued as a Global Debenture will be made to the Depositary;

               (ii)  if any Capital Securities of a series are not
     held by the Clearing Agency or its nominee ("Non-Book-Entry
     Capital Securities"), the Debentures in certificated form of
     the series held by the Trust corresponding to such Capital
     Securities of such series may be presented to the Trustee by
     the Institutional Trustee and any Capital Security
     Certificate which represents such Non-Book-Entry Capital
     Securities will be deemed to represent beneficial interests
     in Debentures so presented to the Trustee by the
     Institutional Trustee having an aggregate principal amount
     equal to the aggregate liquidation amount of such Non-Book-
     Entry Capital Securities until such Capital Security
     Certificates are presented to the Debt Security registrar
     for registration of transfer or reissuance at which time
     such Capital Security Certificates will be canceled and a
     Debenture of the series previously held by the Trust
     registered in the name of the holder of the Capital Security
     Certificate or the transferee of the holder of such Capital
     Security Certificate, as the case may be, with an aggregate
     principal amount equal to the aggregate liquidation amount
     of the Capital Security Certificate canceled, will be
     executed by the Company and delivered to the Trustee for
     authentication and delivery in accordance with the Indenture
     and this First Supplemental Indenture; upon issue of such
     Debentures of such series, Debentures of such series with an
     equivalent aggregate principal amount that were presented by
     the Institutional Trustee to the Trustee will be deemed to
     have been canceled; and

               (iii) prior to the distribution of Debentures
     of a series held by the Institutional Trustee to the holders
     of Trust Securities, the Company and the Trustee shall enter
     into a supplemental indenture pursuant to Article IX of the
     Indenture to provide for transfer procedures and
     restrictions with respect to such Debentures of such series
     substantially similar to those contained in the Declaration
     with respect to Capital Securities of the corresponding
     series to the extent applicable in the circumstances
     existing at the time of distribution of Debentures of such
     series in connection with a Dissolution Event for purposes
     of assuring that no registration of Debentures of such
     series is required under the Securities Act of 1933, as
     amended.

          (b)  A Global Debenture may be transferred, in whole
but not in part, only by the Depositary to a nominee of the
Depositary or by a nominee of the Depositary to the


                                    6
<PAGE> 9

Depositary or another nominee of the Depositary, or to a successor
Depositary selected or approved by the Company or to a nominee of such
successor Depositary.

          (c)  If at any time the Depositary notifies the Company
that it is unwilling or unable to continue as Depositary or if at
any time the Depositary shall no longer be registered or in good
standing under the Securities Exchange Act of 1934, as amended,
or other applicable statute or regulation, and a successor
Depositary is not appointed by the Company within 90 days after
the Company receives such notice or becomes aware of such
condition, as the case may be, the Company will execute, and,
subject to Article II of the Indenture, the Trustee, upon written
request of the Company, will authenticate and make available for
delivery, Debentures of each series in definitive registered form
without coupons, in authorized denominations, and in an aggregage
principal amount equal to the principal amount of the Global
Debenture of such series in exchange for such Global Debenture.
In addition, the Company may at any time determine that the
Debentures of a series shall no longer be represented by a Global
Debenture.  In such event the Company will execute, and subject
to Section 2.07 of the Indenture, the Trustee, upon receipt of an
Officers' Certificate evidencing such determination by the
Company, will authenticate and deliver Debentures of such series
in definitive registered form without coupons, in authorized
denominations, and in an aggregate principal amount equal to the
principal amount of the Global Debenture of such series in
exchange for such Global Debenture.  A Global Debenture shall
also be exchangeable for Debentures in definitive form upon the
occurrence of an Event of Default.  Upon the exchange of a Global
Debenture for Debentures in definitive registered form without
coupons, in authorized denominations, such Global Debenture shall
be canceled by the Trustee.  Such Debentures in definitive
registered form issued in exchange for such Global Debenture
shall be registered in such names and in such authorized
denominations as the Depositary, pursuant to instructions from
its direct or indirect participants or otherwise, shall instruct
the Trustee.  The Trustee shall deliver such Debentures to the
Depositary for delivery to the Persons in whose names such
Debentures are so registered.

          SECTION 2.5
          -----------

          (a)  The Company shall appoint a Calculation Agent,
which may be the Trustee, to determine LIBOR as of the
Determination Date for each quarterly interest period and to
calculate the interest rate and the amount of interest due for
each such interest period.  Absent manifest error, the
Calculation Agents determination of LIBOR and its calculation of
the interest rate for each interest period shall be final and
binding on the holders of the Debentures.

          (b)  The amount of interest payable for any period will
be computed on the basis of the actual number of days elapsed in
a year of twelve 30-day months.  In the event that any date on
which interest is payable on the Debentures of a series is not a
Business Day, then payment of interest payable on such date will
be made on the next succeeding day that is a Business Day (and
without any interest or other payment in respect of any such
delay), except that, if such Business Day is in the next
succeeding calendar year, such payment shall be made on the
immediately preceding Business Day, in each case with the same
force and effect as if made on such date.


                                    7
<PAGE> 10

          (c)  The indebtedness evidenced by all Debentures of a
series is subordinate and junior in right of payment to the prior
payment in full of all present and future Senior Indebtedness and
pari passu in right of payment with all Debentures of each other series.
---- -----

          (d)  If, at any time while the holder of any Debentures
of a series is the Institutional Trustee, the Trust is required
to pay any taxes, duties, assessments or governmental charges of
whatever nature (other than withholding taxes) imposed by the
United States, or any other taxing authority, then, in any such
case, the Company shall pay as additional interest ("Additional
Interest") on the Debentures held by the Institutional Trustee,
such additional amounts as shall be required so that the net
amounts received and retained by the Trust after paying any such
taxes, duties, assessments or other governmental charges will be
equal to the amounts the Trust and the Institutional Trustee
would have received had no such taxes, duties, assessments or
other governmental charges been imposed.

          (e)  If an Initial Debenture is exchanged in a
Registered Exchange Offer prior to the Record Date for the first
Interest Payment Date following such exchange, accrued and unpaid
interest, if any, on such Initial Debenture, up to but not
including the date of issuance of the Exchange Debenture or
Exchange Debentures issued in exchange for such Initial
Debenture, shall be paid on the first Interest Payment Date for
such Exchange Debenture or Exchange Debentures to the
Securityholder or Securityholders of such Exchange Debenture or
Exchange Debentures on the first Record Date with respect to such
Exchange Debenture or Exchange Debentures.  If an Initial
Debenture is exchanged in a Registered Exchange Offer subsequent
to the Record Date for the first Interest Payment Date following
such exchange but on or prior to such Interest Payment Date, then
any such accrued and unpaid interest with respect to such Initial
Debenture and any accrued and unpaid interest on the Exchange
Debenture or Exchange Debentures issued in exchange for such
Initial Debenture, through the day before such Interest Payment
Date, shall be paid on such Interest Payment Date to the
Securityholder of such Initial Debenture on such Record Date.

          (f)  The following terms relate to Special Interest:

               (i)  In the event that either (A) the Exchange
     Offer Registration Statement (as such term is defined in the
     Registration Agreement) is not filed with the Securities and
     Exchange Commission (the "Commission") on or prior to the
     90th day following the Closing Date (as such term is defined
     in the Registration Agreement), (B) the Exchange Offer
     Registration Statement is not declared effective by the
     Commission on or prior to the 120th day following the
     Closing Date or (C) the Registered Exchange Offer (as such
     term is defined in the Registration Agreement) is not
     consummated or a Shelf Registration Statement (as such term
     is defined in the Registration Agreement) with respect to
     the Initial Debentures is not declared effective by the
     Commission on or prior to the 150th day following the
     Closing Date, interest shall accrue (in addition to the
     stated interest on Initial Debentures) from and including
     the next day following each of (1) such 90-day period in the
     case of clause (A) above, (2) such 120-day period in the
     case of clause (B) above and (3) such 150-day period in the
     case of clause (C) above.  In each case, such additional
     interest shall accrue at a rate


                                    8
<PAGE> 11


     per annum equal to 0.25% of the principal amount of the Initial
     Debentures (determined daily).  The aggregate amount of additional
     interest payable pursuant to the above provisions will in no event
     exceed 0.75% per annum of the principal amount of the Initial
     Debentures (determined daily).  Upon (X) the filing of the
     Exchange Offer Registration Statement after the 90-day
     period described in clause (A) above, (Y) the effectiveness
     of the Exchange Offer Registration Statement after the 120-
     day period described in clause (B) above or (Z) the
     consummation of the Registered Exchange Offer or the
     effectiveness of a Shelf Registration Statement, as the case
     may be, after the 150-day period described in clause (C)
     above, the additional interest payable on the Initial
     Debentures, with respect to such clause (A), (B) or (C), as
     the case may be, from the date of such filing, effectiveness
     or consummation, as the case may be, shall cease to accrue.

               (ii)  In the event that a Shelf Registration
     Statement filed with respect to the Initial Debentures is
     declared effective pursuant to the terms of the Registration
     Agreement, if the Company or the Trust fails to keep such
     Shelf Registration Statement continuously effective for the
     period required by the Registration Agreement, then from the
     next day following such time as the Shelf Registration
     Statement is no longer effective until the earlier of
     (A) the date that the Shelf Registration Statement is again
     deemed effective, (B) the date that is the third anniversary
     of the effective date or (C) the date as of which all of the
     Initial Debentures are sold pursuant to the Shelf
     Registration Statement or may be sold without registration
     pursuant to Rule 144 under the Securities Act of 1933,
     interest shall accrue on the Initial Debentures (in addition
     to the stated interest on the Initial Debentures) at a rate
     per annum equal to 0.25% of the principal amount of the
     Initial Debentures (determined daily), to be increased to
     0.50% per annum of the principal amount of the Initial
     Debentures (determined daily) if and when such Shelf
     Registration Statement is no longer effective for 30 days or
     more.

               (iii)  Any additional interest that accrues
     with respect to the Initial Debentures as provided in this
     paragraph is referred to as "Special Interest."  For all
     purposes of the Indenture, this Supplemental Indenture and
     the Initial Debentures, Special Interest shall be treated as
     interest and shall be payable on the same Interest Payment
     Dates and to the Securityholders of record on the same
     record dates as would be the case for stated interest.

          SECTION 2.6
          -----------

          If at any time the holder of all Debentures of a series
ceases to be the Institutional Trustee and, at such time, the
Capital Securities issued by the Trust are rated by at least one
nationally recognized statistical rating agency, then the Company
shall use its best efforts to obtain from at least one nationally
recognized statistical rating agency a rating for the Debentures
of such series.


                                    9
<PAGE> 12

                           ARTICLE III

                  REDEMPTION OF THE DEBENTURES

          SECTION 3.1
          -----------

          If a Tax Event or a Capital Treatment Event shall occur
and be continuing, the Company shall have the right, subject to
the receipt by the Company of prior approval from the Federal
Reserve if then required under applicable capital guidelines or
policies of the Federal Reserve, to redeem, upon not less than 30
days nor more than 60 days' notice, the Debentures in whole or
in part, at any time, within 90 days following the occurrence of
such Tax Event or Capital Treatment Event, as the case may be, at
a redemption price equal to 100% of the principal amount to be
redeemed plus accrued but unpaid interest to the date of such
redemption (the "Redemption Price").  If Debentures are only
partially redeemed pursuant to this Section 3.1, Debentures shall
be redeemed pro rata or by lot or by any other method
            --- ----
utilized by the Trustee. The Redemption Price shall be paid prior
to 11:00 a.m., New York City time, on the date of such redemption
or such earlier time as the Company determines, provided that
                                                --------
the Company shall deposit with the Trustee an amount sufficient
to pay the Redemption Price by 10:00 a.m., New York City time, on
the date the Redemption Price is to be paid.

          SECTION 3.2
          -----------

          At any time on or after February 1, 2007, the Company
shall have the right, subject to the provisions of Article XIV of
the Indenture and to the receipt by the Company of prior approval
from the Federal Reserve if then required under applicable
capital guidelines or policies of the Federal Reserve, to redeem
the Debentures, in whole or in part, from time to time, at the
Redemption Price.  Any redemption pursuant to this Section 3.2
will be made upon not less than 30 days' nor more than 60 days'
notice to the holders of the relevant Debentures.  If Debentures
are only partially redeemed pursuant to this Section 3.2,
Debentures shall be redeemed pro rata or by lot or by any
                             --- ----
other method utilized by the Trustee.  The Redemption Price shall
be paid prior to 11:00 a.m., New York City time, on the date of
such redemption or such earlier time as the Company determines,
provided that the Company shall deposit with the Trustee an
--------
amount sufficient to pay the Redemption Price by 10:00 a.m., New
York City time, on the date the Redemption Price is to be paid.

          The Debentures are not entitled to the benefit of any
sinking fund.

                           ARTICLE IV

              EXTENSION OF INTEREST PAYMENT PERIOD

          SECTION 4.1
          -----------

          The Company shall have the right, subject to the
conditions set forth herein, to defer payments of interest on the
Debentures of a series by extending the interest payment period
on the Debentures of a series at any time and from time to time
during the term of the


                                    10
<PAGE> 13

Debentures, for up to 20 consecutive quarterly periods (each such
extended interest payment period, an "Extension Period"), during which
Extension Period no interest shall be due and payable; provided that
                                                       -------- ----
(i)  no Extension Period may extend beyond the Maturity Date and (ii)
no Extension Period may commence or be extended so long as the Company
is in default in the payment of any interest upon any Debentures of
such series or has not paid all Deferred Interest from a prior
completed Extension Period.  At the termination of an Extension
Period for the Debentures of a series or, if not an Interest
Payment Date, on the Interest Payment Date immediately following
termination of such Extension Period for the Debentures of such
series, the Company shall pay all interest then accrued and
unpaid on the Debentures, together with interest thereon at a
variable annual rate equal to LIBOR plus 0.85%, compounded
quarterly (to the extent permitted by applicable law)
("Compounded Interest") and any Additional Interest (together
with Compounded Interest, "Deferred Interest"), which Deferred
Interest shall be payable to the holders of the Debentures of
such series in whose names the Debentures are registered in the
Debt Security Register on the record date for the payment of
interest on such Interest Payment Date.  Before the termination
of any Extension Period, the Company may further extend such
period, provided that such period together with all such previous
and further consecutive extensions thereof shall not exceed 20
consecutive quarterly periods, or extend beyond the Maturity
Date.  Upon the termination of any Extension Period and upon the
payment of all Deferred Interest then due, the Company may
commence a new Extension Period, subject to the foregoing
requirements.

          SECTION 4.2
          -----------

          (a)  If the Institutional Trustee is the only
registered holder of the Debentures of a series at the time the
Company initiates an Extension Period, the Company shall give
written notice to the Administrators, the Institutional Trustee
and the Trustee of its initiation of such Extension Period one
Business Day before the earlier of (i) the date on which
distributions on the Capital Securities of the corresponding
series are payable, or (ii) the date the Administrators are
required to give notice to holders of the Capital Securities of
the corresponding series (or any national securities exchange or
other organization on which such Capital Securities are listed,
if any) of the record date or the distribution payment date, in
each case with respect to distributions on the Trust Securities
the payment of which is being deferred.

          (b)  If the Institutional Trustee is not the only
registered holder of the Debentures of a series at the time the
Company initiates an Extension Period, the Company shall give the
holders of the Debentures of such series and the Trustee written
notice of its initiation of such Extension Period at least ten
Business Days before the earlier of (i) the next succeeding
Interest Payment Date or (ii) the date the Company is required to
give notice to holders of the Debentures of such series (or any
national securities exchange or other organization on which the
Capital Securities of the corresponding series are listed, if
any) of the record or payment date of such interest, in each case
with respect to interest payments the payment of which is being
deferred.


                                    11
<PAGE> 14

                          ARTICLE V

                   EXPENSES AND GUARANTEE

          SECTION 5.1
          -----------

          In connection with the offering, sale and issuance of
the Debentures of a series and in connection with the sale of any
Trust Securities by the Trust, the Company, in its capacity as
borrower with respect to the Debentures of such series, shall:

          (a)  pay all costs and expenses relating to the
offering, sale and issuance of Debentures of such series,
including commissions to the underwriters payable pursuant to the
Purchase Agreement and compensation of the Trustee under the
Indenture in accordance with the provisions of Section 6.06 of
the Indenture;

          (b)  pay all debts and other obligations (other than
with respect to the Trust Securities) and costs and expenses of
the Trust (including, but not limited to, costs and expenses
relating to the organization of the Trust, the offering, sale and
issuance of the Trust Securities (including commissions to the
underwriters in connection therewith), the fees and expenses, if
any, of the Institutional Trustee, the Delaware Trustee and each
Administrator, the costs and expenses relating to the operation
of the Trust, including, without limitation, costs and expenses
of accountants, attorneys, statistical or bookkeeping services,
expenses for printing and engraving and computing or accounting
equipment, paying agent(s), registrar(s), transfer agent(s),
duplicating, travel and telephone and other telecommunications
expenses and costs and expenses incurred in connection with the
acquisition, financing, and disposition of Trust assets of the
Trust);

          (c)  be primarily and fully liable for any
indemnification obligations arising with respect to the
Declaration or the Purchase Agreement or the Registration
Agreement; and

          (d)  pay any and all taxes, duties, assessments or
governmental charges of whatever nature and all liabilities,
costs and expenses with respect thereto (other than United States
withholding taxes attributable to the Trust or assets of the
Trust) to which the Trust may become subject.

          SECTION 5.2
          -----------

          Upon termination of the Declaration or the removal or
resignation of the Delaware Trustee or the Institutional Trustee,
as the case may be, pursuant to Section 5.7 of the Declaration,
the Company shall pay to the Delaware Trustee or the
Institutional Trustee, as the case may be, all amounts owing to
the Delaware Trustee or the Institutional Trustee, as the case
may be, under Sections 10.4 and 10.6 of the Declaration accrued
to the date of such termination, removal or resignation.


                                    12
<PAGE> 15

                         ARTICLE VI

                     FORM OF DEBENTURE

          The Debentures and the Trustees certificate of
authentication to be endorsed thereon are to be substantially in
the following forms and are expressly made a part of this First
Supplemental Indenture:

                    (FACE OF DEBENTURE)

          [IF THE DEBENTURE IS TO BE A GLOBAL DEBENTURE, INSERT:
This Debenture is a Global Debenture within the meaning of the
Indenture hereinafter referred to and is registered in the name
of a Depositary or a nominee of a Depositary.  This Debenture is
exchangeable for Debentures of this series registered in the name
of a person other than the Depositary or its nominee only in the
limited circumstances described in the Indenture, and no transfer
of this Debenture may be registered except in limited
circumstances.  Except as otherwise provided in Section 2.11 of
the Indenture, this Debenture may be transferred, in whole but
not in part, only to another nominee of the Depositary or to a
successor Depositary or to a nominee of such successor
Depositary.

          Unless this Debenture is presented by an authorized
representative of The Depository Trust Company (55 Water Street,
New York, New York) to the issuer or its agent for registration
of transfer, exchange or payment, and any Debenture of this
series issued is registered in the name of Cede & Co. or such
other name as requested by an authorized representative of The
Depository Trust Company and any payment hereon is made to Cede &
Co., ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR
OTHERWISE BY A PERSON IS WRONGFUL since the registered owner
hereof, Cede & Co., has an interest herein.]

          [IF THIS DEBENTURE IS ONE OF A SERIES ORIGINALLY ISSUED
PURSUANT TO AN EXEMPTION FROM REGISTRATION UNDER THE SECURITIES
ACT, AS SPECIFIED PURSUANT TO SECTION 2.03 OF THE INDENTURE,
INSERT THE FOLLOWING UNLESS OTHERWISE DETERMINED BY THE COMPANY -
- THIS DEBENTURE HAS NOT BEEN REGISTERED UNDER THE U.S.
SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT") OR ANY
STATE SECURITIES LAWS.  NEITHER THIS DEBENTURE NOR ANY INTEREST
OR PARTICIPATION HEREIN MAY BE REOFFERED, SOLD, ASSIGNED,
TRANSFERRED, PLEDGED, ENCUMBERED OR OTHERWISE DISPOSED OF IN THE
ABSENCE OF SUCH REGISTRATION UNLESS SUCH TRANSACTION IS EXEMPT
FROM, OR NOT SUBJECT TO, THE REGISTRATION REQUIREMENTS OF THE
SECURITIES ACT.  THE HOLDER OF THIS DEBENTURE BY ITS ACCEPTANCE
HEREOF AGREES TO OFFER, SELL OR OTHERWISE TRANSFER SUCH DEBENTURE
PRIOR TO THE DATE WHICH IS THREE YEARS AFTER THE LATER OF THE
ORIGINAL ISSUE DATE HEREOF AND THE LAST DATE ON WHICH MERCANTILE
BANCORPORATION INC. (THE "COMPANY") OR ANY AFFILIATE OF THE
COMPANY WAS THE OWNER OF THIS DEBENTURE OR ANY PREDECESSOR OF
THIS DEBENTURE (THE "RESALE RESTRICTIONS TERMINATION DATE") ONLY

                                    13

<PAGE> 16

(A) TO THE COMPANY, (B) PURSUANT TO AN EFFECTIVE REGISTRATION
STATEMENT UNDER THE SECURITIES ACT, (C) FOR SO LONG AS THE
DEBENTURES ARE ELIGIBLE FOR RESALE PURSUANT TO RULE 144A UNDER
THE SECURITIES ACT ("RULE 144A"), TO A PERSON IT REASONABLY
BELIEVES IS A "QUALIFIED INSTITUTIONAL BUYER" AS DEFINED IN RULE
144A THAT PURCHASES FOR ITS OWN ACCOUNT OR FOR THE ACCOUNT OF A
QUALIFIED INSTITUTIONAL BUYER TO WHOM NOTICE IS GIVEN THAT THE
TRANSFER IS BEING MADE IN RELIANCE ON RULE 144A, (D) TO AN
INSTITUTIONAL "ACCREDITED INVESTOR" WITHIN THE MEANING OF
SUBPARAGRAPH (a) (1), (2), (3) OR (7) OF RULE 501 UNDER THE
SECURITIES ACT THAT IS ACQUIRING THE DEBENTURE FOR ITS OWN
ACCOUNT OR FOR THE ACCOUNT OF SUCH AN INSTITUTIONAL "ACCREDITED
INVESTOR," FOR INVESTMENT PURPOSES AND NOT WITH A VIEW TO, OR FOR
OFFER OR SALE IN CONNECTION WITH, ANY DISTRIBUTION IN VIOLATION
OF THE SECURITIES ACT OR (E) PURSUANT TO ANOTHER AVAILABLE
EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES
ACT, SUBJECT TO THE COMPANYS RIGHT PRIOR TO ANY SUCH OFFER, SALE
OR TRANSFER PURSUANT TO CLAUSES (D) OR (E) TO REQUIRE THE
DELIVERY OF AN OPINION OF COUNSEL, CERTIFICATION AND/OR OTHER
INFORMATION SATISFACTORY TO IT IN ACCORDANCE WITH THE INDENTURE,
A COPY OF WHICH MAY BE OBTAINED FROM THE COMPANY.  THE HOLDER OF
THIS DEBENTURE AGREES THAT IT WILL COMPLY WITH THE FOREGOING
RESTRICTIONS.  DEBENTURES OWNED BY A PURCHASER THAT IS NOT A
QUALIFIED INSTITUTIONAL BUYER MAY NOT BE HELD IN BOOK-ENTRY FORM.
THIS LEGEND WILL BE REMOVED UPON THE REQUEST OF A HOLDER AFTER
THE RESALE RESTRICTIONS TERMINATION DATE.]

No.
    ---------------------


               MERCANTILE BANCORPORATION INC.
        FLOATING RATE JUNIOR SUBORDINATED DEFERRABLE
                INTEREST DEBENTURE DUE 2027

          MERCANTILE BANCORPORATION INC., a Missouri corporation
(the "Company," which term includes any successor corporation
under the Indenture hereinafter referred to), for value received,
hereby promises to pay to ------------ or registered assigns, the
principal sum of ---------------- Dollars ($--------- ) on
February 1, 2027, and to pay interest on said principal sum from
February 4, 1997, or from the most recent interest payment date
(each such date, an "Interest Payment Date") to which interest
has been paid or duly provided for, quarterly (subject to
deferral as set forth herein) in arrears on the first day of
February, May, August and November of each year commencing May 1,
1997, at a variable annual rate equal to LIBOR plus 0.85% until
the principal hereof shall have become due and payable, and on
any overdue principal and (without duplication and to the extent
that payment of such interest is enforceable under applicable
law) on any overdue installment of interest at a variable annual
rate equal to LIBOR plus 0.85% compounded quarterly.  The amount
of interest payable on any Interest Payment Date shall be
computed on the basis of the actual number of


                                    14
<PAGE> 17

days elapsed in a year of twelve 30-day months.  In the event that any
date on which interest is payable on this Debenture is not a Business
Day, then payment of interest payable on such date will be made
on the next succeeding day that is a Business Day (and without
any interest or other payment in respect of any such delay),
except that, if such Business Day is in the next succeeding
calendar year, such payment shall be made on the immediately
preceding Business Day, in each case with the same force and
effect as if made on such date.  The interest installment 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 Debenture (or one or more
Predecessor Securities, as defined in said Indenture) is
registered at the close of business on the Record Date for such
interest installment, [which shall be the close of business on
the Business Day next preceding such Interest Payment Date].  [IF
PURSUANT TO THE PROVISIONS OF THE INDENTURE THE DEBENTURES OF
THIS SERIES ARE NO LONGER REPRESENTED SOLELY BY A GLOBAL
DEBENTURE, SUBSTITUTE THE FOLLOWING FOR THE FOREGOING BRACKETED
TEXT -- which shall be the close of business on the 15th day next
preceding such Interest Payment Date.]  Any such interest
installment not punctually paid or duly provided for shall
forthwith cease to be payable to the registered holders on such
Record Date and may be paid to the Person in whose name this
Debenture (or one or more Predecessor Securities) is registered
at the close of business on a special record date to be fixed by
the Trustee for the payment of such defaulted interest, notice
whereof shall be given to the registered holders of this series
of Debentures not less than 10 days prior to such special record
date, or may be paid at any time in any other lawful manner not
inconsistent with the requirements of any securities exchange on
which the Debentures 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.  In the event the Debentures of this
series are issued in non-book entry form, the principal of and
interest on this Debenture shall be payable at the office or
agency of the Trustee (or other paying agent appointed by the
Company) maintained for that purpose in any coin or currency of
the United States of America that at the time of payment is legal
tender for payment of public and private debts; provided,
                                                --------
however, that payment of interest may be made at the option
-------
of the Company by check mailed to the registered holder at such
address as shall appear in the Debt Security Register or by wire
transfer to an account appropriately designated by the holder
hereof.  Notwithstanding the foregoing, so long as the holder of
this Debenture is the Institutional Trustee, the payment of the
principal of and interest on this Debenture will be made in
immediately available funds at such place and to such account as
may be designated by the Institutional Trustee.

          The indebtedness evidenced by this Debenture is, to the
extent provided in the Indenture, subordinate and junior in right
of payment to the prior payment in full of all Senior
Indebtedness, and this Debenture is issued subject to the
provisions of the Indenture with respect thereto.  Each holder of
this Debenture, by accepting the same, (a) agrees to and shall be
bound by such provisions, (b) authorizes and directs the Trustee
on his or her behalf to take such action as may be necessary or
appropriate to acknowledge or effectuate the subordination so
provided and (c) appoints the Trustee his or her attorney-in-fact
for any and all such purposes.  Each holder hereof, by his or her
acceptance hereof, hereby waives all notice of the acceptance of
the subordination provisions contained herein and in the
Indenture by each holder of Senior


                                    15
<PAGE> 18

Indebtedness, whether now outstanding or hereafter incurred, and waives
reliance by each such holder upon said provisions.

          If this Debenture is exchanged in a Registered Exchange
Offer prior to the Record Date for the first Interest Payment
Date following such exchange, accrued and unpaid interest, if
any, on this Debenture, up to but not including the date of
issuance of the Exchange Debenture or Exchange Debentures issued
in exchange for this Debenture, shall be paid on the first
Interest Payment Date for such Exchange Debenture or Exchange
Debentures to the Securityholder or Securityholders of such
Exchange Debenture or Exchange Debentures on the first Record
Date with respect to such Exchange Debenture or Exchange
Debentures.  If this Debenture is exchanged in a Registered
Exchange Offer subsequent to the Record Date for the first
Interest Payment Date following such exchange but on or prior to
such Interest Payment Date, then any such accrued and unpaid
interest with respect to this Debenture and any accrued and
unpaid interest on the Exchange Debenture or Exchange Debentures
issued in exchange for this Debenture, through the day before
such Interest Payment Date, shall be paid on such Interest
Payment Date to the Securityholder of this Debenture on such
Record Date.

          If any time the Trust shall be required to pay any
taxes, duties, assessments or governmental charges of whatever
nature (other than withholding taxes) imposed by the United
States or any other taxing authority, then, in any such case, the
Company shall pay as additional interest on the Debentures held
by the Institutional Trustee such additional amounts as shall be
required so that the net amounts received and retained by the
Trust after paying any such taxes, duties, assessments or other
governmental charges will equal the amounts the Trust and the
Institutional Trustee would have received had no such taxes,
duties, assessments or other governmental charges been imposed.
[IF THIS DEBENTURE IS AN INITIAL DEBENTURE INSERT -- In addition,
the interest rate payable on the Debentures of this series is
subject to increase as provided in the Indenture if, pursuant to
the Registration Agreement either (A) the Exchange Offer
Registration Statement (as such term is defined in the
Registration Agreement) is not filed with the Securities and
Exchange Commission (the "Commission") on or prior to the 90th
day following the Closing Date (as such term is defined in the
Registration Agreement), (B) the Exchange Offer Registration
Statement is not declared effective by the Commission on or prior
to the 120th day following the Closing Date or (C) the Registered
Exchange Offer (as such term is defined in the Registration
Agreement) is not consummated or a Shelf Registration Statement
(as such term is defined in the Registration Agreement) with
respect to the Initial Debentures is not declared effective by
the Commission on or prior to the 150th day following the Closing
Date.

          The interest rate payable on the Debentures of this
series is also subject to adjustment in certain circumstances if
a Shelf Registration Statement filed pursuant to the Registration
Agreement is not kept continuously effective for a specified
period, as provided in the Indenture.]

          This Debenture shall not be entitled to any benefit
under the Indenture hereinafter referred to, be valid or become
obligatory for any purpose until the certificate of
authentication hereon shall have been signed by or on behalf of
the Trustee.


                                    16
<PAGE> 19

          The provisions of this Debenture are continued on the
reverse side hereof and such continued provisions shall for all
purposes have the same effect as though fully set forth at this
place.


                                    17
<PAGE> 20

          IN WITNESS WHEREOF, the Company has caused this
instrument to be executed.

Dated
      --------------------
                                MERCANTILE BANCORPORATION INC.

                                By:
                                    -------------------------
                                    Name:
                                    Title:

[Seal]
                                By:
                                    -------------------------
                                    Name:
                                    Title:

                 CERTIFICATE OF AUTHENTICATION
                 -----------------------------


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



                             THE CHASE MANHATTAN BANK, as Trustee

                             By
                                ------------------------------
                                     Authorized Officer


                                    18
<PAGE> 21

                     (REVERSE OF DEBENTURE)
                     ----------------------

          This Debenture is one of a duly authorized series of
Debt Securities of the Company, all issued or to be issued in one
or more series under and pursuant to an Indenture dated as of
February 4, 1997, duly executed and delivered between the Company
and The Chase Manhattan Bank, as Trustee (the "Trustee"), as
supplemented by the First Supplemental Indenture dated as of
February 4, 1997, between the Company and the Trustee (the
Indenture as so supplemented, the "Indenture"), to which
Indenture and all indentures supplemental thereto reference is
hereby made for a description of the rights, limitations of
rights, obligations, duties and immunities thereunder of the
Trustee, the Company and the holders of the series of Debt
Securities (referred to herein as the "Debentures") of which this
Debenture is a part.  The summary of the terms of this Debenture
contained herein does not purport to be complete and is qualified
by reference to the Indenture.  By the terms of the Indenture,
the Debt Securities are issuable in series that may vary as to
amount, date of maturity, rate of interest and in other respects
as provided in the Indenture.  This series of Debentures is
limited in aggregate principal amount as specified in said First
Supplemental Indenture.

          Upon the occurrence and continuation of a Tax Event or
a Capital Treatment Event, this Debenture may become due and
payable, in whole or in part, at any time, within 90 days
following the occurrence of such Tax Event or Capital Treatment
Event, as the case may be, at a redemption price equal to 100% of
the principal amount being redeemed together with any accrued and
unpaid interest thereon.  The Company shall also have the right
to redeem this Debenture at the option of the Company, in whole
or in part, at any time or from time to time on or after February
1, 2007, at par plus accrued and unpaid interest to the
redemption date.

          Any redemption pursuant to the preceding paragraph will
be made, subject to the receipt by the Company of prior approval
from the Board of Governors of the Federal Reserve System (the
"Federal Reserve") if then required under applicable capital
guidelines or policies of the Federal Reserve, upon not less than
30 days' nor more than 60 days' notice.  If the Debentures are
only partially redeemed by the Company, the Debentures will be
redeemed pro rata or by lot or by any other method utilized
         --- ----
by the Trustee; provided that if, at the time of redemption,
                --------
the Debentures are registered as a Global Debenture, the
Depositary shall determine the principal amount of such
Debentures held by each of its direct participants to be redeemed
pro rata in accordance with its procedures.
--- ----

          In the event of redemption of this Debenture in part
only, a new Debenture or Debentures of this series for the
unredeemed portion hereof will be issued in the name of the
holder hereof upon the cancellation hereof.

          In case an Event of Default, as defined in the
Indenture, shall have occurred and be continuing, the principal
of all of the Debentures may be declared due and payable, and
upon such declaration of acceleration shall become due and
payable, in the manner, with the effect and subject to the
conditions provided in the Indenture.

          The Indenture contains provisions permitting the
Company and the Trustee, with the consent of the holders of not
less than a majority in aggregate principal amount of the Debt


                                    19
<PAGE> 22

Securities of any series at the time outstanding affected
thereby, as specified in the Indenture, to execute supplemental
indentures for the purpose of adding any provisions to or
changing in any manner or eliminating any of the provisions of
the Indenture or of any supplemental indenture or of modifying in
any manner the rights of the holders of the Debt Securities;
provided, however, that no such supplemental indenture
--------  -------
shall, among other things, without the consent of the holders of
each Debt Security then outstanding and affected thereby (i)
extend the fixed maturity of any Debt Securities of any series,
or reduce the principal amount thereof or any redemption premium
thereon, or reduce the rate or extend the time of payment of
interest thereon, or make the principal of, or interest or
premium on, the Debt Securities payable in any coin or currency
other than that provided in the Debt Securities, or impair or
affect the right of any holder of Debt Securities to institute
suit for the payment thereof, or (ii) reduce the aforesaid
percentage of Debt Securities, the holders of which are required
to consent to any such supplemental indenture.  The Indenture
also contains provisions permitting the holders of a majority in
aggregate principal amount of the Debt Securities of a series at
the time outstanding affected thereby as provided in the
Indenture, on behalf of all of the holders of the Debt Securities
of such series, to waive any past default in the performance of
any of the covenants contained in the Indenture, or established
pursuant to the Indenture with respect to such series, and its
consequences, except a default in the payment of the principal of
or premium, if any, or interest on any of the Debt Securities of
such series.  Any such consent or waiver by the registered holder
of this Debenture (unless revoked as provided in the Indenture)
shall be conclusive and binding upon such holder and upon all
future holders and owners of this Debenture and of any Debenture
issued in exchange herefor or in place hereof (whether by
registration of transfer or otherwise), irrespective of whether
or not any notation of such consent or waiver is made upon this
Debenture.

          No reference herein to the Indenture and no provision
of this Debenture or of the Indenture shall alter or impair the
obligation of the Company, which is absolute and unconditional,
to pay the principal of and premium, if any, and interest on this
Debenture at the time and place and at the rate and in the money
herein prescribed.

          The Company shall have the right at any time during the
term of the Debentures and from time to time, subject to certain
conditions, to defer payment of interest on the Debentures of a
series by extending the interest payment period for Extension
Periods, each not exceeding 20 consecutive quarterly periods as
provided in the Indenture.  Notwithstanding the foregoing, no
Extension Period may extend beyond the maturity date of the
Debentures.  In the event that the Company exercises its right to
extend an interest payment period, then during any Extension
Period (a) the Company shall not declare or pay any dividends on,
make any distribution with respect to, or redeem, purchase,
acquire, or make a liquidation payment with respect to, any of
its capital stock or rights to acquire such capital stock (other
than (i) purchases or acquisitions of shares of any such capital
stock or rights to acquire such capital stock in connection with
the satisfaction by the Company of its obligations under any
employee benefit plans, (ii) as a result of a reclassification of
the Company's capital stock or rights to acquire such capital
stock or the exchange or conversion of one class or series of the
Company's capital stock or rights to acquire such capital stock
for another class or series of the Company's capital stock or
rights to acquire such capital stock, (iii) the purchase of
fractional interests in shares of the Company's capital stock pursuant
to the conversion or exchange provisions of such capital stock


                                    20
<PAGE> 23

or the security being converted or exchanged, (iv) dividends and
distributions made on the Company's capital stock or rights to acquire
such capital stock with the Company's capital stock or rights to
acquire such capital stock, or (v) any declaration of a dividend in
connection with the implementation of a shareholder rights plan, or the
issuance of stock under any such plan in the future, or the redemption
or repurchase of any such rights pursuant thereto), or make guarantee
payments (other than payments under the Capital Securities Guarantee or
the Common Securities Guarantee for the Trust) with respect to the
foregoing and (b) the Company shall not make any payment of
interest, principal or premium, if any, on or repay, repurchase
or redeem any debt securities issued by the Company that rank
pari passu with or junior to the Debentures.  Prior to
---- -----
the termination of any such Extension Period, the Company may
further defer payments of interest by extending the interest
payment period; provided, however, that each such
                --------  -------
Extension Period, including all such previous and further
extensions thereof, may not exceed 20 consecutive quarterly
periods or extend beyond the maturity of the Debentures.  Upon
the termination of any Extension Period and the payment of all
amounts then due, the Company may commence a new Extension
Period, subject to the terms set forth in the Indenture.  No
interest during an Extension Period, except on the date on which
such Extension Period terminates (or if such date is not an
Interest Payment Date, on the immediately following Interest
Payment Date), shall be due and payable.

          As provided in the Indenture and subject to certain
limitations herein and therein set forth, this Debenture is
transferable by the registered holder hereof on the Debt Security
Register of the Company, upon surrender of this Debenture for
registration of transfer at the office or agency of the Trustee
in the City and State of New York accompanied by a written
instrument or instruments of transfer in form satisfactory to the
Company or the Trustee duly executed by the registered holder
hereof or his attorney duly authorized in writing, and thereupon
one or more new Debentures of authorized denominations and for
the same aggregate principal amount and series will be issued to
the designated transferee or transferees.  No service charge will
be made for any such registration of transfer, but the Company
may require payment of a sum sufficient to cover any tax or other
governmental charge payable in relation thereto.

          Prior to due presentment for registration of transfer
of this Debenture, the Company, the Trustee, any Authenticating
Agent, any paying agent, any transfer agent and the Debt Security
registrar may deem and treat the registered holder hereof as the
absolute owner hereof (whether or not this Debenture shall be
overdue and notwithstanding any notice of ownership or writing
hereon) for the purpose of receiving payment of or on account of
the principal hereof and interest due hereon and for all other
purposes, and neither the Company nor the Trustee nor any
Authenticating Agent nor any paying agent nor any transfer agent
nor any Debt Security registrar shall be affected by any notice
to the contrary.

          No recourse shall be had for the payment of the
principal of or the interest on this Debenture, or for any claim
based hereon, or otherwise in respect hereof, or based on or in
respect of the Indenture, against any incorporator, stockholder,
officer or director, past, present or future, as such, of the
Company or of any predecessor or successor corporation, whether
by virtue of any constitution, statute or rule of law, or by the
enforcement of any assessment or


                                    21
<PAGE> 24

penalty or otherwise, all such liability being, by the acceptance
hereof and as part of the consideration for the issuance hereof,
expressly waived and released.

          The Debentures of this series are issuable only in
registered form without coupons.  A Global Debenture is
exchangeable for Debentures in definitive form only under certain
limited circumstances set forth in the Indenture.  As provided in
the Indenture and subject to certain limitations herein and
therein set forth, Debentures of this series are exchangeable for
a like aggregate principal amount of Debentures of this series of
a different authorized denomination, as requested by the holder
surrendering the same.

          [IF THIS DEBENTURE IS AN INITIAL DEBENTURE INSERT --
The Debentures of this series are issuable only in minimum
denominations of $100,000 and any integral multiple of $1,000 in
excess thereof.  The Debentures of this series may be transferred
only in blocks having an aggregate principal amount of not less
than $100,000.  Any transfer of Debentures of this series in a
block having an aggregate principal amount of less than $100,000
shall be deemed to be void and of no legal effect whatsoever.
Any transferee of Debentures of this series having an aggregate
principal amount of less than $100,000 shall be deemed not to be
the holder of such Debentures for any purpose, including, but not
limited to, the receipt of payments on such Debentures, and such
transferee shall be deemed to have no interest whatsoever in such
Debentures.]

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

          THE INTERNAL LAWS OF THE STATE OF NEW YORK SHALL GOVERN
THE INDENTURE AND THE DEBENTURES, WITHOUT REGARD TO CONFLICT OF
LAWS PRINCIPLES THEREOF.

                         ARTICLE VII

                        MISCELLANEOUS

          SECTION 7.1
          -----------

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

          SECTION 7.2
          -----------

          The recitals herein contained are made by the Company
and not by the Trustee, and the Trustee assumes no responsibility
for the correctness thereof.  The Trustee makes no representation
as to the validity or sufficiency of this First Supplemental
Indenture.


                                    22
<PAGE> 25

          SECTION 7.3
          -----------

          This First Supplemental Indenture and each Debenture
shall be deemed to be a contract made under the internal laws of
the State of New York, and for all purposes shall be construed in
accordance with the laws of said State without regard to conflict
of laws principles thereof.

          SECTION 7.4
          -----------

          In case any one or more of the provisions contained in
this First Supplemental Indenture or in a series of Debentures
shall for any reason be held to be invalid, illegal or
unenforceable in any respect, such invalidity, illegality or
unenforceability shall not affect any other provisions of this
First Supplemental Indenture or of such series of the Debentures,
but this First Supplemental Indenture and such series of the
Debentures shall be construed as if such invalid or illegal or
unenforceable provision had never been contained herein or
therein.

          This First Supplemental Indenture may be executed in
any number of counterparts each of which shall be an original;
but such counterparts shall together constitute but one and the
same instrument.


                                    23
<PAGE> 26

          IN WITNESS WHEREOF, the parties hereto have caused this
First Supplemental Indenture to be duly executed as of the day
and year first above written.

                                MERCANTILE BANCORPORATION INC.

                                By:
                                    --------------------------
                                    Name:
                                    Title:

                                THE CHASE MANHATTAN BANK, as
                                   Trustee

                                By:
                                    --------------------------
                                    Name:
                                    Title:


                                    24