Exhibit 4(b)

                        SUB-INVESTMENT ADVISORY AGREEMENT

            AGREEMENT dated September 29, 2006, between BlackRock Advisors, LLC,
a Delaware limited liability company (the "Advisor"), and BlackRock Investment
Management International Limited, a corporation organized under the laws of
Scotland (the "Sub-Advisor").

            WHEREAS, the Advisor has agreed to furnish investment advisory
services to the BlackRock Master International Portfolio (the "Fund"), a series
of BlackRock Master Trust, a Delaware statutory trust (the "Trust"), an open-end
management investment company registered under the Investment Company Act of
1940, as amended (the "1940 Act");

            WHEREAS, the Advisor wishes to retain the Sub-Advisor to provide it
with certain sub-advisory services as described below in connection with
Advisor's advisory activities on behalf of the Fund;

            WHEREAS, the advisory agreement between the Advisor and the Trust,
dated September 29, 2006 (such agreement or the most recent successor agreement
between such parties relating to advisory services to the Trust is referred to
herein as the "Advisory Agreement") contemplates that the Advisor may
sub-contract investment advisory services with respect to the Funds to a
sub-advisor pursuant to a sub-advisory agreement agreeable to the Trust and
approved in accordance with the provisions of the 1940 Act; and

            WHEREAS, this Agreement has been approved in accordance with the
provisions of the 1940 Act, and the Sub-Advisor is willing to furnish such
services upon the terms and conditions herein set forth; and

            NOW, THEREFORE, in consideration of the mutual premises and
covenants herein contained and other good and valuable consideration, the
receipt of which is hereby acknowledged, it is agreed by and between the parties
hereto as follows:

      1. Appointment. The Advisor hereby appoints the Sub-Advisor to act as
sub-advisor with respect to the Fund and the Sub-Advisor accepts such
appointment and agrees to render the services herein set forth for the
compensation herein provided.

      2. Services of the Sub-Advisor. Subject to the succeeding provisions of
this section, the oversight and supervision of the Advisor and the direction and
control of the Trust's Board of Trustees, the Sub-Advisor will perform certain
of the day-to-day operations of the Fund, which may include one or more of the
following services, at the request of the Advisor: (a) acting as investment
advisor for and managing the investment and reinvestment of those assets of the
Fund as the Advisor may from time to time request and in connection therewith
have complete discretion in purchasing and selling such securities and other
assets for the Fund and in voting, exercising consents and exercising all other
rights appertaining to such securities and other assets on behalf of the Fund;
(b) arranging, subject to the provisions of paragraph 3 hereof, for the purchase
and sale of securities and other assets of the Fund; (c) providing investment
research and credit analysis concerning the Fund's investments, (d) assist the
Advisor in determining what portion of the Fund's assets will be invested in
cash, cash equivalents and money market instruments, (e) placing orders for all
purchases and sales of such investments made for the Fund, and


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(f) maintaining the books and records as are required to support Fund investment
operations. At the request of the Advisor, the Sub-Advisor will also, subject to
the oversight and supervision of the Advisor and the direction and control of
the Trust's Board of Trustees, provide to the Advisor or the Fund any of the
facilities and equipment and perform any of the services described in Section 3
of the Advisory Agreement. In addition, the Sub-Advisor will keep the Fund and
the Advisor informed of developments materially affecting the Fund and shall, on
its own initiative, furnish to the Fund from time to time whatever information
the Sub-Advisor believes appropriate for this purpose. The Sub-Advisor will
periodically communicate to the Advisor, at such times as the Advisor may
direct, information concerning the purchase and sale of securities for the Fund,
including: (a) the name of the issuer, (b) the amount of the purchase or sale,
(c) the name of the broker or dealer, if any, through which the purchase or sale
is effected, (d) the CUSIP number of the instrument, if any, and (e) such other
information as the Advisor may reasonably require for purposes of fulfilling its
obligations to the Fund under the Advisory Agreement. The Sub-Advisor will
provide the services rendered by it under this Agreement in accordance with the
Fund's investment objectives, policies and restrictions (as currently in effect
and as they may be amended or supplemented from time to time) as stated in the
Fund's Prospectus and Statement of Additional Information and the resolutions of
the Trust's Board of Trustees.

      3. Covenants. (a) In the performance of its duties under this Agreement,
the Sub-Advisor shall at all times conform to, and act in accordance with, any
requirements imposed by: (i) the provisions of the 1940 Act and the Investment
Advisers Act of 1940, as amended (the "Advisers Act"), and all applicable Rules
and Regulations of the Securities and Exchange Commission (the "SEC"); (ii) any
other applicable provision of law; (iii) the provisions of the Agreement and
Declaration of Trust and By-Laws of the Trust, as such documents are amended
from time to time; (iv) the investment objectives and policies of the Fund as
set forth in its Registration Statement on Form N-1A and/or the resolutions of
the Board of Trustees; and (v) any policies and determinations of the Board of
the Trustees of the Trust and

            (b) In addition, the Sub-Advisor will:

                  (i) place orders either directly with the issuer or with any
broker or dealer. Subject to the other provisions of this paragraph, in placing
orders with brokers and dealers, the Sub-Advisor will attempt to obtain the best
price and the most favorable execution of its orders. In placing orders, the
Sub-Advisor will consider the experience and skill of the firm's securities
traders as well as the firm's financial responsibility and administrative
efficiency. Consistent with this obligation, the Sub-Advisor may select brokers
on the basis of the research, statistical and pricing services they provide to
the Fund and other clients of the Advisor or the Sub-Advisor. Information and
research received from such brokers will be in addition to, and not in lieu of,
the services required to be performed by the Sub-Advisor hereunder. A commission
paid to such brokers may be higher than that which another qualified broker
would have charged for effecting the same transaction, provided that the
Sub-Advisor determines in good faith that such commission is reasonable in terms
either of the transaction or the overall responsibility of the Advisor and the
Sub-Advisor to the Fund's and their other clients and that the total commissions
paid by the Fund will be reasonable in relation to the benefits to the Fund over
the long-term. Subject to the foregoing and the provisions of the 1940 Act, the
Securities


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Exchange Act of 1934, as amended, and other applicable provisions of law, the
Advisor may select brokers and dealers with which it or the Trust is affiliated;

                  (ii) maintain books and records with respect to the Fund's
securities transactions and will render to the Advisor and the Trust's Board of
Trustees such periodic and special reports as they may request;

                  (iii) maintain a policy and practice of conducting its
investment advisory services hereunder independently of the commercial banking
operations of its affiliates. When the Sub-Advisor makes investment
recommendations for the Fund, its investment advisory personnel will not inquire
or take into consideration whether the issuer of securities proposed for
purchase or sale for the Fund's account are customers of the commercial
department of its affiliates; and

                  (iv) treat confidentially and as proprietary information of
the Fund all records and other information relative to the Fund, and the Fund's
prior, current or potential shareholders, and will not use such records and
information for any purpose other than performance of its responsibilities and
duties hereunder, except after prior notification to and approval in writing by
the Fund, which approval shall not be unreasonably withheld and may not be
withheld where the Sub-Advisor may be exposed to civil or criminal contempt
proceedings for failure to comply, when requested to divulge such information by
duly constituted authorities, or when so requested by the Fund.

      4. Services Not Exclusive. Nothing in this Agreement shall prevent the
Sub-Advisor or any officer, employee or other affiliate thereof from acting as
investment advisor for any other person, firm or corporation, or from engaging
in any other lawful activity, and shall not in any way limit or restrict the
Sub-Advisor or any of its officers, employees or agents from buying, selling or
trading any securities for its or their own accounts or for the accounts of
others for whom it or they may be acting; provided, however, that the
Sub-Advisor will undertake no activities which, in its judgment, will adversely
affect the performance of its obligations under this Agreement.

      5. Books and Records. In compliance with the requirements of Rule 31a-3
under the 1940 Act, the Sub-Advisor hereby agrees that all records which it
maintains for the Trust are the property of the Trust and further agrees to
surrender promptly to the Trust any such records upon the Trust's request. The
Sub-Advisor further agrees to preserve for the periods prescribed by Rule 31a-2
under the 1940 Act the records required to be maintained by Rule 31a-1 under the
1940 Act (to the extent such books and records are not maintained by the
Advisor).

      6. Expenses. During the term of this Agreement, the Sub-Advisor will bear
all costs and expenses of its employees and any overhead incurred by the
Sub-Advisor in connection with its duties hereunder; provided that the Board of
Trustees of the Trust may approve reimbursement to the Sub-Advisor of the
pro-rata portion of the salaries, bonuses, health insurance, retirement benefits
and all similar employment costs for the time spent on Fund operations
(including, without limitation, compliance matters) (other than the provision of
investment advice and administrative services required to be provided hereunder)
of all


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personnel employed by the Sub-Advisor who devote substantial time to the Fund
operations or the operations of other investment companies advised or
sub-advised by the Sub-Advisor.

      7. Compensation.

            (a) The Advisor agrees to pay to the Sub-Advisor and the Sub-Advisor
agrees to accept as full compensation for all services rendered by the
Sub-Advisor as such, a monthly fee in arrears at an annual rate equal to the
amount set forth in Schedule A hereto. For any period less than a month during
which this Agreement is in effect, the fee shall be prorated according to the
proportion which such period bears to a full month of 28, 29, 30 or 31 days, as
the case may be.

            (b) For purposes of this Agreement, the Net Assets of the Fund shall
be calculated pursuant to the procedures adopted by resolutions of the Trustees
of the Trust for calculating the value of the Fund's assets or delegating such
calculations to third parties.

      8. Indemnity.

            (a) The Fund hereby agrees to indemnify the Sub-Advisor and each of
the Sub-Advisor's directors, officers, employees, agents, associates and
controlling persons and the directors, partners, members, officers, employees
and agents thereof (including any individual who serves at the Sub-Advisor's
request as director, officer, partner, member, trustee or the like of another
entity) (each such person being an "Indemnitee") against any liabilities and
expenses, including amounts paid in satisfaction of judgments, in compromise or
as fines and penalties, and counsel fees (all as provided in accordance with
applicable state law) reasonably incurred by such Indemnitee in connection with
the defense or disposition of any action, suit or other proceeding, whether
civil or criminal, before any court or administrative or investigative body in
which such Indemnitee may be or may have been involved as a party or otherwise
or with which such Indemnitee may be or may have been threatened, while acting
in any capacity set forth herein or thereafter by reason of such Indemnitee
having acted in any such capacity, except with respect to any matter as to which
such Indemnitee shall have been adjudicated not to have acted in good faith in
the reasonable belief that such Indemnitee's action was in the best interest of
the Trust and furthermore, in the case of any criminal proceeding, so long as
such Indemnitee had no reasonable cause to believe that the conduct was
unlawful; provided, however, that (1) no Indemnitee shall be indemnified
hereunder against any liability to the Trust or the Fund or its shareholders or
any expense of such Indemnitee arising by reason of (i) willful misfeasance,
(ii) bad faith, (iii) gross negligence or (iv) reckless disregard of the duties
involved in the conduct of such Indemnitee's position (the conduct referred to
in such clauses (i) through (iv) being sometimes referred to herein as
"disabling conduct"), (2) as to any matter disposed of by settlement or a
compromise payment by such Indemnitee, pursuant to a consent decree or
otherwise, no indemnification either for said payment or for any other expenses
shall be provided unless there has been a determination that such settlement or
compromise is in the best interests of the Fund and that such Indemnitee appears
to have acted in good faith in the reasonable belief that such Indemnitee's
action was in the best interest of the Fund and did not involve disabling
conduct by such Indemnitee and (3) with respect to any action, suit or other
proceeding voluntarily prosecuted by any Indemnitee as plaintiff,
indemnification shall be mandatory only if


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the prosecution of such action, suit or other proceeding by such Indemnitee was
authorized by a majority of the full Board of Trustees of the Trust.

            (b) The Fund shall make advance payments in connection with the
expenses of defending any action with respect to which indemnification might be
sought hereunder if the Trust receives a written affirmation of the Indemnitee's
good faith belief that the standard of conduct necessary for indemnification has
been met and a written undertaking to reimburse the Fund unless it is
subsequently determined that such Indemnitee is entitled to such indemnification
and if the Trustees of the Trust determine that the facts then known to them
would not preclude indemnification. In addition, at least one of the following
conditions must be met: (A) the Indemnitee shall provide a security for such
Indemnitee-undertaking, (B) the Trust shall be insured against losses arising by
reason of any unlawful advance, or (C) a majority of a quorum consisting of
Trustees of the Trust who are neither "interested persons" of the Trust (as
defined in Section 2(a)(19) of the 1940 Act) nor parties to the proceeding
("Disinterested Non-Party Trustees") or an independent legal counsel in a
written opinion, shall determine, based on a review of readily available facts
(as opposed to a full trial-type inquiry), that there is reason to believe that
the Indemnitee ultimately will be found entitled to indemnification.

            (c) All determinations with respect to indemnification hereunder
shall be made (1) by a final decision on the merits by a court or other body
before whom the proceeding was brought that such Indemnitee is not liable by
reason of disabling conduct, or (2) in the absence of such a decision, by (i) a
majority vote of a quorum of the Disinterested Non-Party Trustees of the Trust,
or (ii) if such a quorum is not obtainable or even, if obtainable, if a majority
vote of such quorum so directs, independent legal counsel in a written opinion.
All determinations that advance payments in connection with the expense of
defending any proceeding shall be authorized shall be made in accordance with
the immediately preceding clause (2) above.

            The rights accruing to any Indemnitee under these provisions shall
not exclude any other right to which such Indemnitee may be lawfully entitled.

      9. Limitation on Liability. The Sub-Advisor will not be liable for any
error of judgment or mistake of law or for any loss suffered by the Advisor or
by the Fund in connection with the performance of this Agreement, except a loss
resulting from a breach of fiduciary duty with respect to the receipt of
compensation for services or a loss resulting from willful misfeasance, bad
faith or gross negligence on its part in the performance of its duties or from
reckless disregard by it of its duties under this Agreement.

      10. Duration and Termination. This Agreement shall become effective as of
the date hereof and, unless sooner terminated with respect to the Fund as
provided herein, shall continue in effect for a period of two years. Thereafter,
if not terminated, this Agreement shall continue in effect with respect to the
Fund for successive periods of 12 months, provided such continuance is
specifically approved at least annually by both (a) the vote of a majority of
the Trust's Board of Trustees or a vote of a majority of the outstanding voting
securities of the Fund at the time outstanding and entitled to vote and (b) by
the vote of a majority of the Trustees, who are not parties to this Agreement or
interested persons (as such term is defined in the 1940 Act) of any such party,
cast in person at a meeting called for the purpose of voting on such approval.


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Notwithstanding the foregoing, this Agreement may be terminated by the Trust, on
behalf of the Fund, or the Advisor at any time, without the payment of any
penalty, upon giving the Sub-Advisor 60 days' notice (which notice may be waived
by the Sub-Advisor), provided that such termination by the Trust or the Advisor
shall be directed or approved by the vote of a majority of the Trustees of the
Trust in office at the time or by the vote of the holders of a majority of the
voting securities of the Fund at the time outstanding and entitled to vote, or
by the Sub-Advisor on 60 days' written notice (which notice may be waived by the
Trust, on behalf of the Fund, and the Advisor), and will terminate automatically
upon any termination of the Advisory Agreement between the Trust and the
Advisor. This Agreement will also immediately terminate in the event of its
assignment. (As used in this Agreement, the terms "majority of the outstanding
voting securities," "interested person" and "assignment" shall have the same
meanings of such terms in the 1940 Act.)

      11. Notices. Any notice under this Agreement shall be in writing to the
other party at such address as the other party may designate from time to time
for the receipt of such notice and shall be deemed to be received on the earlier
of the date actually received or on the fourth day after the postmark if such
notice is mailed first class postage prepaid.

      12. Amendment of this Agreement. This Agreement may be amended by the
parties only if such amendment is specifically approved by the vote of the Board
of Trustees of the Trust, including a majority of those Trustees who are not
parties to this Agreement or interested persons of any such party cast in person
at a meeting called for the purpose of voting on such approval and, where
required by the 1940 Act, by a vote of a majority of the outstanding voting
securities of the Fund.

      13. Miscellaneous. The captions in this Agreement are included for
convenience of reference only and in no way define or delimit any of the
provisions hereof or otherwise affect their construction or effect. If any
provision of this Agreement shall be held or made invalid by a court decision,
statute, rule or otherwise, the remainder of this Agreement shall not be
affected thereby. This Agreement shall be binding on, and shall inure to the
benefit of the parties hereto and their respective successors.

      14. Governing Law. This Agreement shall be governed by and construed in
accordance with the laws of the State of New York for contracts to be performed
entirely therein without reference to choice of law principles thereof and in
accordance with the applicable provisions of the 1940 Act. To the extent that
the applicable laws of the State of New York, or any of the provisions, conflict
with the applicable provisions of the 1940 Act, the latter shall control.

      15. Counterparts. This Agreement may be executed in counterparts by the
parties hereto, each of which shall constitute an original counterpart, and all
of which, together, shall constitute one Agreement.


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      IN WITNESS WHEREOF, the parties hereto have caused this instrument to be
executed by their duly authorized officers designated below as of the day and
year first above written.

                                                 BLACKROCK ADVISORS, LLC

                                                 By: ___________________________
                                                     Name:  Donald C. Burke
                                                     Title: Managing Director

                                                 BLACKROCK INVESTMENT MANAGEMENT
                                                 INTERNATIONAL LIMITED

                                                 By: ___________________________
                                                     Name:
                                                     Title:

Agreed and Accepted:

BLACKROCK MASTER TRUST

By: ________________________________
    Name:  Donald C. Burke
    Title: Vice President & Treasurer


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                                   Schedule A

                           Sub-Investment Advisory Fee

74.00% of the monthly advisory fee received by the Advisor from the Fund.


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