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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 July 10, 2003

      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 July 10, 2003 (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 July 10, 2003 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 July 10, 2003 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 July 10, 2003 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 July 10, 2003 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 July 10, 2003 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 July 10, 2003 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 July 10, 2003 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 July 10, 2003 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 July 10, 2003 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 July 10, 2003 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 July 10, 2003 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 July 10, 2003 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 in each
      case for (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 July 10, 2003 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 July 10, 2003 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 July 10, 2003 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 July 10, 2003.

                                          CITIGROUP GLOBAL MARKETS HOLDINGS INC.

                                          By: /s/ Mark I. Kleinman
                                             ----------------------------------

                                             Name: Mark I. Kleinman
                                             Title:Executive Vice President and
                                                   Treasurer

Attest:

By:  s/ Douglas C. Turnbull
   -------------------------------

   Name: Douglas C. Turnbull
   Title:Assistant Secretary

                                          DEUTSCHE BANK TRUST COMPANY AMERICAS

                                          By: /s/ Yana Kalachikova
                                             ----------------------------------

                                             Name: Yana Kalachikova
                                             Title: Associated

Attest:

By: /s/ Dorothy Robinson
   --------------------------------

   Name:  Dorothy Robinson
   Title: Vice President

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