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                                                                    EXHIBIT 4(u)

                     CITIGROUP GLOBAL MARKETS HOLDINGS INC.

                                       and

                      DEUTSCHE BANK TRUST COMPANY AMERICAS,
                                   as Trustee

                          SIXTH SUPPLEMENTAL INDENTURE

                        Dated as of ___________ __, 20__

     Supplemental Indenture to the Indenture dated as of December 1, 1988,
      providing for the issuance of series of subordinated debt securities

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                  SIXTH SUPPLEMENTAL INDENTURE, dated as of ___________ __, 20__
(the "Sixth Supplemental Indenture"), between Citigroup Global Markets Holdings
Inc., a corporation duly organized and existing under the laws of the State of
New York and formerly known as Salomon Smith Barney Holdings Inc. (the
"Company"), and Deutsche Bank Trust Company Americas, a corporation duly
organized and existing under the laws of the State of New York and formerly
known as Bankers Trust Company, as Trustee (the "Trustee"), under the Indenture
dated as of December 1, 1988 (the "Original Indenture") as supplemented by the
First Supplemental Indenture, dated September 7, 1990, the Second Supplemental
Indenture, dated December 14, 1993, the Third Supplemental Indenture, dated July
3, 1996, the Fourth Supplemental Indenture, dated November 28, 1997, and the
Fifth Supplemental Indenture, dated July 1, 1999 (collectively the "Supplemental
Indentures"). The Supplemental Indentures together with the Original Indenture
are herein referred to as the "Indenture." Capitalized terms used but not
defined herein shall have the meanings ascribed thereto under the Indenture.

                  WHEREAS, the parties hereto have previously entered into the
Indenture to provide for the issuance of and sale by the Company from time to
time of its subordinated debt securities (the "Debt Securities"); and

                  WHEREAS, Section 1101(10) of the Indenture provides that the
Company, when authorized by a Board Resolution, and the Trustee, at any time and
from time to time, may enter into an indenture supplemental to the Indenture, in
form satisfactory to the Trustee, without the consent of any holder of Debt
Securities, to cure any ambiguity, to correct or supplement any provision
therein that may be defective or inconsistent with any other provision therein,
or to make any other provisions with respect to matters or questions under the
Indenture that shall not be inconsistent with any provision of the Indenture,
provided that such other provisions shall not adversely affect the interests of
the Holders of Outstanding Debt Securities or Coupons, if any, of any series
created prior to the execution of such supplemental indenture in any material
respect; and

                  WHEREAS, Section 1101(5) of the Indenture authorizes the
Company and the Trustee, without the consent of any holder of Debt Securities,
to enter into a supplemental indenture to change or eliminate any of the
provisions of this Indenture, provided that any such change or elimination shall
become effective only when there is no Outstanding Debt Security or Coupon of
any series created prior to the execution of such supplemental indenture that is
entitled to the benefit of such provision and as to which such supplemental
indenture would apply; and

                  WHEREAS, the Company has changed its name from "Salomon Smith
Barney Holdings Inc." to "Citigroup Global Markets Holdings Inc."; and

                  WHEREAS, the Company, pursuant to the foregoing authority,
proposes in and by this Sixth Supplemental Indenture to amend the Indenture in
certain respects; and

                  WHEREAS, the Company has duly authorized the execution and
delivery of this Sixth Supplemental Indenture, and all things necessary have
been done to make this Sixth Supplemental Indenture a valid agreement of the
Company, in accordance with its terms;

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                  NOW, THEREFORE, the Company and the Trustee hereby agree as
follows:

                                    ARTICLE I

                  In the first paragraph of the Indenture, the words "SALOMON
SMITH BARNEY HOLDINGS INC." shall be replaced with "CITIGROUP GLOBAL MARKETS
HOLDINGS INC."

                                   ARTICLE II

                  Section 2.01. Section 501 of the Indenture shall be amended as
to Debt Securities originally issued on or after ___________ __, 20__ by
deleting such section in its entirety and substituting therefor the following:

         Section 501. Events of Default.

                  "Event of Default" wherever used herein with respect to Debt
         Securities of any series means any one of the following events
         (whatever the reason for such Event of Default and whether it shall be
         voluntary or involuntary or be effected by operation of law, pursuant
         to any judgment, decree or order of any court or any order, rule or
         regulation of any administrative or governmental body):

                  (1) the entry of a decree or order for relief in respect of
         the Company by a court having jurisdiction in the premises in an
         involuntary case under the Federal bankruptcy laws, as now or hereafter
         constituted, or any other applicable Federal or State bankruptcy,
         insolvency or other similar law, or appointing a receiver, liquidator,
         assignee, custodian, trustee, sequestrator (or other similar official)
         of the Company or of any substantial part of its property, or ordering
         the winding up or liquidation of its affairs, and the continuance of
         any such decree or order unstayed and in effect for a period of 90
         consecutive days; or

                  (2) the commencement by the Company of a voluntary case under
         the Federal bankruptcy laws, as now or hereafter constituted, or any
         other applicable Federal or State bankruptcy, insolvency or other
         similar law, or the consent by it to the entry of an order for relief
         in an involuntary case under any such law or to the appointment of a
         receiver, liquidator, assignee, custodian, trustee, sequestrator (or
         other similar official) of the Company or of any substantial part of
         its property, or the making by it of an assignment for the benefit of
         its creditors, or the admission by it in writing of its inability to
         pay its debts generally as they become due, or the taking of corporate
         action by the Company in furtherance of any such action.

                  Section 2.02. Section 502 of the Indenture shall be amended as
to Debt Securities originally issued on or after ___________ __, 20__ by
deleting such section in its entirety and substituting therefor the following:

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         Section 502. Acceleration of Maturity; Rescission and Annulment.

                  If an Event of Default with respect to Debt Securities of any
         series at the time Outstanding occurs and is continuing, then in every
         such case the Trustee or the Holders of not less than 25% in principal
         amount of Outstanding Debt Securities of such series may declare the
         principal amount (or, if any Debt Securities of such series are
         Discount Securities, such portion of the principal amount of such
         Discount Securities as may be specified in the terms of such Discount
         Securities) of and all accrued but unpaid interest on all the Debt
         Securities of such series to be due and payable immediately, by a
         notice in writing to the Company (and to the Trustee if given by
         Holders), and upon any such declaration such principal amount (or
         specified amount) and interest shall become immediately due and
         payable. Upon payment of such amounts in the Currency in which such
         Debt Securities are denominated (except as otherwise provided pursuant
         to Section 301), all obligations of the Company in respect of the
         payment of principal of and interest on the Debt Securities of such
         series shall terminate.

                  At any time after such a declaration of acceleration with
         respect to Debt Securities of any series has been made and before a
         judgment or decree for payment of the money due has been obtained by
         the Trustee as hereinafter in this Article provided, the Holders of a
         majority in principal amount of the Outstanding Debt Securities of such
         series, by written notice to the Company and the Trustee, may rescind
         and annul such declaration and its consequences if the Company has paid
         or deposited with the Trustee a sum in the Currency in which such Debt
         Securities are denominated (except as otherwise provided pursuant to
         Section 301) sufficient to pay

                           (A) all overdue installments of interest on all Debt
                  Securities of such series or all overdue payments with respect
                  to any related Coupons,

                           (B) the principal of (and premium, if any, on) any
                  Debt Securities of such series that have become due otherwise
                  than by such declaration of acceleration and interest thereon
                  at the rate or rates prescribed therefor in such Debt
                  Securities,

                           (C) to the extent that payment of such interest is
                  lawful, interest upon overdue installments of interest on each
                  Debt Security or upon overdue payments on any Coupons at the
                  rate or rates prescribed therefor in such Debt Securities or
                  Coupons, and

                           (D) all sums paid or advanced by the Trustee
                  hereunder and the reasonable compensation, expenses,
                  disbursements and advances of the Trustee, its agents and
                  counsel; provided, however, that all sums payable under this
                  clause (D) shall be paid in Dollars.

         No such rescission and waiver shall affect any subsequent default or
         impair any right consequent thereon.

                  For all purposes under this Indenture, if a portion of the
         principal of any Discount Securities shall have been accelerated and
         declared due and payable pursuant to the provisions hereof, then, from
         and after such declaration, unless such declaration has been

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         rescinded and annulled, the principal amount of such Discount
         Securities shall be deemed, for all purposes hereunder, to be such
         portion of the principal thereof as shall be due and payable as a
         result of such acceleration, and payment of such portion of the
         principal thereof as shall be due and payable as a result of such
         acceleration, together with interest, if any, thereon and all other
         amounts owing thereunder, shall constitute payment in full of such
         Discount Securities.

                                   ARTICLE III

                  Section 3.01. Section 507 of the Indenture shall be renamed
"Limitations on Suits; Default" and amended as to Debt Securities originally
issued on or after ___________ __, 20__ by inserting the following at the end
thereof:

                  The following events shall be "Defaults" with respect to any
         such Debt Securities under this Indenture:

                  (A) an Event of Default with respect to such series specified
         in Section 501; or

                  (B) default in the payment of any interest upon any Debt
         Security of such series or any payment with respect to the related
         Coupons, if any, when it becomes due and payable, and continuance of
         such default for a period of 30 days, whether or not such payment is
         prohibited by Article Sixteen hereof; or

                  (C) default in the payment of the principal of (or premium, if
         any, on) any Debt Security of such series at its Maturity, whether or
         not such payment is prohibited by Article Sixteen hereof; or

                  (D) default in the deposit of any sinking fund payment, when
         and as due by the terms of any Debt Security of such series, whether or
         not such payment is prohibited by Article Sixteen hereof; or

                  (E) default in the performance, or breach, of any covenant or
         warranty of the Company in this Indenture (other than a covenant or
         warranty a default in whose performance or whose breach is elsewhere in
         this Section specifically dealt with or which expressly has been
         included in this Indenture solely for the benefit of Debt Securities of
         a series other than such series) or established in or pursuant to the
         Board Resolution or supplemental indenture, as the case may be,
         pursuant to which the Debt Securities of such series were issued as
         contemplated by Section 301, and continuance of such default or breach
         for a period of 60 days after there has been given, by registered or
         certified mail, to the Company by the Trustee or to the Company and the
         Trustee by the Holders of at least 25% in principal amount of the
         Outstanding Debt Securities of such series, a written notice specifying
         such default or breach and requiring it to be remedied and stating that
         such notice is a "Notice of Default" hereunder; or

                  (F) any other Default provided with respect to Debt Securities
         of that series pursuant to Section 301.

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                  Section 3.02. In the Indenture, as amended hereby, excepting
Section 101, Section 301(17), Section 501, Section 502 and Section 507(A), the
words "Event of Default" and "Events of Default" shall be replaced as to Debt
Securities originally issued on or after ________ ___, 20__ with "Default" and
"Defaults," respectively.

                  Section 3.03. Section 513 of the Indenture shall be amended as
to Debt Securities originally issued on or after ________ ___, 20__ by deleting
such section in its entirety and substituting therefor the following:

         Section 513. Waiver of Past Defaults.

                  Prior to any declaration of acceleration with respect to such
         series under Section 502, the Holders of not less than a majority in
         principal amount of the Outstanding Debt Securities of any series may
         on behalf of the Holders of all the Debt Securities of any such series
         and any related Coupons waive any past default hereunder with respect
         to such series and its consequences, except a default

                           (1) not theretofore cured in the payment of the
                  principal of (or premium, if any) or interest on any Debt
                  Security of such series or in the payment of any related
                  Coupon; or

                           (2) in respect of a covenant or provision hereof that
                  under Article Eleven cannot be modified or amended without the
                  consent of the Holder of each Outstanding Debt Security of
                  such series affected.

                  Upon any such waiver, such default shall cease to exist, and
         any Default arising therefrom shall be deemed to have been cured, for
         every purpose of the Debt Securities of such series under this
         Indenture, but no such waiver shall extend to any subsequent or other
         default or impair any right consequent thereon.

                  Section 3.04. Section 101 of the Indenture shall be amended as
to Debt Securities originally issued on or after ________ ___, 20__ by inserting
the following after the twenty-first paragraph thereof:

         "Default" has the meaning specified in Section 507.

                  Section 3.05. Section 301(17) of the Indenture shall be
amended as to Debt Securities originally issued on or after ________ ___, 20__
by deleting such section in its entirety and substituting therefor the
following:

                  (17) any additional Events of Default or Defaults or
         restrictive covenants provided for with respect to Debt Securities of
         the series; and


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                                   ARTICLE IV

                  Section 1001 of the Indenture shall be amended as to Debt
Securities originally issued on or after ________ ___, 20__ by deleting such
section in its entirety and substituting therefor the following:

         Section 1001.  Company May Consolidate, etc. Only on Certain Terms.

                  The Company shall not consolidate with or merge into any other
         corporation or convey, transfer or lease its properties and assets
         substantially as an entirety to any Person, unless:

                           (1) the corporation formed by such consolidation or
                  into which the Company is merged or the Person which acquires
                  by conveyance or transfer, or which leases, the properties and
                  assets of the Company substantially as an entirety (the
                  "successor corporation") shall expressly assume, by an
                  indenture supplemental hereto, executed and delivered to the
                  Trustee, in form satisfactory to the Trustee, the due and
                  punctual payment of the principal of (and premium, if any) and
                  interest (including all additional interest, if any, payable
                  pursuant to Section 1202) on all the Debt Securities and the
                  due and punctual payment of any Coupons and the performance of
                  every covenant of this Indenture on the part of the Company to
                  be performed or observed;

                           (2) immediately after giving effect to such
                  transaction and treating any indebtedness that becomes an
                  obligation of the Company as a result of such transaction as
                  having been incurred by the Company at the time of such
                  transaction, no Default, and no event that, after notice or
                  lapse of time, or both, would become a Default, shall have
                  happened or be continuing; and

                           (3) the Company has delivered to the Trustee an
                  Officers' Certificate and an Opinion of Counsel each stating
                  that such consolidation, merger, conveyance, transfer or lease
                  and such supplemental indenture comply with this Article and
                  that all conditions precedent herein provided for relating to
                  such transaction have been complied with.

                                    ARTICLE V

                  Section 5.01. Section 1303 of the Indenture shall be amended
as to Debt Securities originally issued on or after ________ ___, 20__ by
inserting the following after the first sentence thereof:

         Notwithstanding anything to the contrary herein, if then required under
         applicable capital adequacy guidelines, regulations or policies of the
         Federal Reserve, the Company may not redeem, repay or repurchase any
         Debt Securities prior to maturity without the prior approval of the
         Federal Reserve.


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                  Section 5.02. Section 1502 of the Indenture shall be amended
as to Debt Securities originally issued on or after ________ __, 20__ by
inserting the following after the third paragraph thereof:

                  Notwithstanding anything to the contrary herein, if then
         required under applicable capital adequacy guidelines, regulations or
         policies of the Federal Reserve, the Company may not be deemed to have
         been Discharged in respect of any Debt Securities prior to maturity
         without the prior approval of the Federal Reserve.

                  Section 5.03. Section 101 of the Indenture, as amended
hereby, shall be amended as to Debt Securities originally issued on or after
________ __, 20__ by inserting the following after the thirtieth paragraph
thereof:

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

                  Section 101 of the Indenture shall be amended as to Debt
Securities originally issued on or after ________ __, 20__ by deleting the
fifty-third paragraph thereof in its entirety and substituting therefor the
following:

                  "Senior Indebtedness" means the following indebtedness or
         obligations, whether outstanding at the date of execution of this
         Indenture or thereafter incurred, assumed, guaranteed or otherwise
         created: (i) the principal, premium, if any, and interest in respect of
         (A) indebtedness of the Company for money borrowed and (B) indebtedness
         evidenced by securities, notes, debentures, bonds or other similar
         instruments issued by the Company; (ii) all capital lease obligations
         of the Company and any synthetic lease or tax retention operating
         lease; (iii) all obligations of the Company issued or assumed as the
         deferred purchase price of property, all conditional sale obligations
         of the Company and all obligations of the Company under any conditional
         sale or title retention agreement (but excluding trade accounts payable
         in the ordinary course of business); (iv) all obligations, contingent
         or otherwise, of the Company in respect of any letters of credit,
         banker's acceptance, security purchase facilities and similar credit
         transactions; (v) all obligations of the Company in respect of interest
         rate swap, cap or other agreements, interest rate future or options
         contracts, currency swap agreements, currency future or option
         contracts and other similar agreements; (vi) all obligations of the
         type referred to in clauses (i) through (v) of other persons for the
         payment of which the Company is responsible or liable as obligor,
         guarantor or otherwise; and (vii) all obligations of the type referred
         to in clauses (i) through (vi) of other persons secured by any lien on
         any property or asset of the Company (whether or not such obligation is
         assumed by the Company), except for in each case (1) the Debt
         Securities or any appurtenant Coupons, (2) any such indebtedness that
         is by its terms subordinated to or pari passu with the Debt Securities,
         (3) any junior subordinated debt of the Company that is by its terms
         subordinated to the Debt Securities, (4) any guarantee now or hereafter
         entered into by the Company in respect of any junior subordinated debt,
         trust preferred securities or preferred or preference stock that is by
         its terms subordinated to the Debt Securities and

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         (5) all other debt securities and guarantees in respect of junior
         subordinated debt securities issued to any trust, or a trustee of such
         trust, partnership or other entity affiliated with the Company which
         is a financing vehicle of the Company (a "Financing Entity") in
         connection with the issuance by such Financing Entity of preferred
         securities or other securities guaranteed by the Company pursuant to
         an instrument that ranks junior to the Debt Securities.

                                   ARTICLE VII

                  Section 7.01. (a) Section 1601 of the Indenture shall be
amended as to Debt Securities originally issued on or after ________ __, 20__ by
deleting the first paragraph of such section in its entirety and substituting
therefor the following:

                  The Company covenants and agrees, and each Holder of a Debt
         Security or Coupon, by his acceptance thereof, likewise covenants and
         agrees, that the indebtedness represented by the Debt Securities and
         any Coupons and the payment of the principal of (and premium, if any)
         and interest on each and all of the Debt Securities and the payment of
         any Coupons is hereby expressly subordinated, to the extent and in the
         manner hereinafter set forth, in right of payment to the prior payment
         in full of Senior Indebtedness.

                  (b) Section 1601(b) of the Indenture shall be amended as to
Debt Securities originally issued on or after ________ __, 20__ by deleting such
clause in its entirety and substituting therefor the following:

         (b) that (i) a default shall have occurred with respect to the payment
         of principal of (or premium, if any) or interest on or other monetary
         amounts due and payable on any Senior Indebtedness, or (ii) there shall
         have occurred an event of default (other than a default in the payment
         of principal, premium, if any, or interest, or other monetary amounts
         due and payable) in respect of any Senior Indebtedness, as defined
         therein or in the instrument under which the same is outstanding,
         permitting the holder or holders thereof to accelerate the maturity
         thereof (with notice or lapse of time, or both), and such event of
         default shall have continued beyond the period of grace, if any, in
         respect thereof, and, in the cases of subclauses (i) and (ii) of this
         clause (b), such default or event of default shall not have been cured
         or waived or shall not have ceased to exist, or

                  Section 7.02. Section 1602 of the Indenture shall be amended
as to Debt Securities originally issued on or after ________ __, 20__ by
deleting such section in its entirety and substituting therefor the following:

         Section 1602. [Reserved].

                                  ARTICLE VIII

                  Section 8.01. The Trustee accepts the trusts created by this
Sixth Supplemental Indenture upon the terms and conditions set forth in the
Indenture. The Trustee shall not be

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responsible or accountable in any manner whatsoever for or in respect of, and
makes no representation with respect to, the validity or sufficiency of this
Sixth Supplemental Indenture or the due execution hereof by the Company and
shall not be responsible in any manner whatsoever for or in respect of the
correctness of the recitals and statements contained herein, all of which
recitals and statements are made solely by the Company.

                  Section 8.02. Except as amended as set forth above, the
Indenture is in all respects ratified and confirmed and the terms, provisions
and conditions thereof shall remain in full force and effect. This Sixth
Supplemental Indenture shall take effect on the date hereof.

                  Section 8.03. This Sixth Supplemental Indenture may be
executed in any number of counterparts, each of which shall be deemed to be an
original for all purposes, but such counterparts shall together be deemed to
constitute but one and the same instrument.

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                  IN WITNESS WHEREOF, each of Citigroup Global Markets Holdings
Inc. and Deutsche Bank Trust Company Americas, as Trustee, has caused this Sixth
Supplemental Indenture to be signed and acknowledged by one of its officers
thereunto duly organized, and its corporate seal to be affixed hereto, and the
same to be attested by the signature of its Secretary or one of its Assistant
Secretaries, all as of ________ __, 20__.

                                          CITIGROUP GLOBAL MARKETS HOLDINGS INC.

                                          By: ______________________________

                                              Name:
                                              Title:

Attest:

By: __________________________________

    Name:
    Title:

                                          DEUTSCHE BANK TRUST COMPANY AMERICAS

                                          By: ______________________________

                                              Name:
                                              Title:

Attest:

By: __________________________________

    Name:
    Title:

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