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                                                                     Exhibit 9



                        [SHEARMAN & STERLING LETTERHEAD]





                               September 14, 2001



Mercury U.S. Large Cap Fund of
Mercury Funds, Inc.
P.O. Box 9011
Princeton, NJ 08543-9011

Ladies and Gentlemen:

            Mercury Funds, Inc. (the "Corporation") is authorized to issue and
sell 11,000,000,000 shares of common stock (the "Shares"), par value $.0001 per
share, of which 600,000,000 Shares are designated as Shares of the Mercury U.S.
Large Cap Fund series (the "Fund"), in the manner and on the terms set forth in
the Fund's current Registration Statement on Form N-1A, being filed with the
Securities and Exchange Commission (File Nos. 333-66481 and 811-08797) (the
"Registration Statement") together with this opinion as an exhibit thereto.


            We have, as counsel, participated in certain proceedings relating to
the Corporation and to the Shares. We have examined copies, either certified or
otherwise proved to our satisfaction to be genuine, of the Corporation's
Articles of Incorporation, as amended and restated to date, and its By-Laws, as
amended and restated and as currently in effect, and other documents relating to
its organization and operation as we have deemed necessary and appropriate as a
basis for this opinion. We have assumed the authenticity of all instruments and
documents, and the conformity to original documents of all instruments and
documents submitted to us as certified, conformed or photostatic copies. In
addition, we have received a certificate dated August 31, 2001 of the Maryland
State Department of Assessments and Taxation (the "Certificate") that the
Corporation is in good standing under the laws of the State of Maryland. We have
also reviewed the Registration Statement filed as of the date of this opinion.


            Our opinion in paragraph 1 with regard to the valid existence of the
Corporation in the State of Maryland, its state of incorporation, is based
solely upon the Certificate.

            Based upon the foregoing and in reliance thereon and subject to the
assumptions, limitations and qualifications set forth herein, it is our opinion
that:

            1.    The Corporation has been duly incorporated and is validly
                  existing under
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                  the laws of the State of Maryland.

            2.    The Corporation is authorized to issue up to 11 billion
                  (11,000,000,000) Shares, of which 600,000,000 Shares are
                  designated as Shares of the Fund. Under Maryland law, (a) the
                  number of Shares may be increased or decreased by action of
                  the Board of Directors, and (b) the Shares that are issued and
                  subsequently redeemed by the Corporation are, by virtue of
                  such redemption, restored to the status of authorized and
                  unissued Shares.

            3.    Subject to the continuing effectiveness of the Registration
                  Statement and compliance with applicable state securities laws
                  (as to either of which we express no opinion), and assuming
                  the continued valid existence of the Corporation under the
                  laws of the State of Maryland, upon the issuance of the Shares
                  for a consideration not less than the par value thereof as
                  required by the laws of the State of Maryland, and for the net
                  asset value thereof as required by the Investment Company Act
                  of 1940, as amended, and in accordance with the terms of the
                  Registration Statement, such Shares will be legally issued and
                  outstanding and fully paid and non-assessable.

            We hereby consent to the filing of this opinion with the Securities
and Exchange Commission as a part of the Registration Statement and with any
state securities commission where such filing is required. We also consent to
the reference to our firm as counsel in the prospectus and statement of
additional information filed as a part thereof. In giving this consent we do not
admit that we come within the category of persons whose consent is required
under Section 7 of the Securities Act of 1933, as amended.

            We are members of the Bar of the State of New York. The opinions
expressed herein are based solely on our review of the Maryland General
Corporation Law, and, where applicable, published cases, rules or regulations
relating thereto.

                                                Very truly yours,

                                                /s/ SHEARMAN & STERLING

                                                SHEARMAN & STERLING

S&S: MKN:JHY:PJS