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                                                                     EXHIBIT 5.1

                                                   [MAYER BROWN ROWE & MAW LOGO]

July 24, 2003                                       Mayer, Brown, Rowe & Maw LLP
                                                       190 South La Salle Street
                                                    Chicago, Illinois 60603-3441
RefcoFund Holdings, LLC
  as general partner of S&P Managed Futures              Main Tel (312) 782-0600
  Index Fund, LP                                         Main Fax (312) 701-7711
550 W. Jackson                                            www.mayerbrownrowe.com
Suite 1300
 Chicago, Illinois 60661


Ladies and Gentlemen:

     We have acted as counsel to S&P Managed Futures Index Fund, LP, a Delaware
limited partnership (the "Partnership"), and its general partner, RefcoFund
Holdings, LLC, a Delaware limited liability company (the "General Partner"), in
connection with the preparation and filing of a registration statement on Form
S-1 (the "Registration Statement") with the Securities and Exchange Commission
under the Securities Act of 1933, as amended (the "Act") on or about July 25,
2003. The Registration Statement relates to the offering of up to $100,000,000
in aggregate amount of units of limited partnership interest (together, the
"Units").

     In rendering this opinion, we have relied, to the extent we deem such
reliance proper, as to matters of fact, without investigation, upon certificates
of public officials and others and upon affidavits, certificates and written
statements of officers and employees of, and accountants for, the Partnership
and the General Partner. We have also examined originals or copies, certified or
otherwise identified to our satisfaction, of such instruments, documents and
records as we have deemed relevant and necessary to examine for the purpose of
this opinion, including (a) the Registration Statement, including the exhibits
thereto, (b) the Certificate of Limited Partnership of the Partnership, (c) the
Limited Partnership Agreement of the Partnership (the "Limited Partnership
Agreement"); and (d) the form of Selling Agreement (the "Selling Agreement").

     In rendering this opinion, we have assumed the legal capacity of all
natural persons executing the documents and records that we have reviewed, the
accuracy and completeness of all documents and records that we have reviewed,
the genuineness of all signatures, the authenticity of the documents submitted
to us as originals and the conformity to authentic original documents of all
documents submitted to us as certified, conformed or reproduced copies. In
making our examination of documents executed or to be executed by parties other
than the General Partner or the Partnership, we have assumed that such parties
had or will have the power, corporate or other, to enter into and perform all
obligations thereunder and have also assumed the due authorization by all
requisite action, and execution and delivery by such parties of such documents
and the validity and binding effect thereof.


     Brussels Charlotte Chicago Cologne Frankfurt Houston London Los Angeles
              Manchester New York Palo Alto Paris Washington, D.C.
Independent Mexico City Correspondent: Jauregui, Navarrete, Nader y Rojas, S.C.

    Mayer, Brown, Rowe & Maw LLP operates in combination with our associated
       English limited liability partnership in the offices listed above.

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     This opinion is limited to the Delaware Revised Uniform Limited Partnership
Act ("DRULPA"), and we have not considered and express no opinion on any other
laws of the state of Delaware or the laws of any other jurisdiction, including
federal laws and rules and regulations relating thereto. Our opinions are
rendered only with respect to DRULPA which is in effect on the date of this
opinion. This opinion is given as of the date hereof and we assume no obligation
to advise you of changes that may hereafter be brought to our attention.

     Based upon and subject to the foregoing, it is our opinion that, assuming
(i) the due authorization, execution and delivery to the General Partner of the
subscription agreement and power of attorney and the subscription requirements
acknowledgment (collectively, the "Subscription Agreement") by each subscriber
for Units (the "Subscribers") and all parties thereto other than the General
Partner, (ii) the due acceptance by the General Partner of the admission of the
Subscribers as limited partners of the Partnership to the Partnership, (iii) the
payment by each Subscriber to the Partnership of the full consideration due from
it for the Units subscribed to by it, (iv) that the books and records of the
Partnership will set forth all information required by the Limited Partnership
Agreement and the Delaware Revised Uniform Limited Partnership Act, including
all information with respect to all persons and entities to be admitted as
partners and their contributions to the Partnership, (v) that the Subscribers,
as limited partners of the Partnership, do not participate in the control of the
business of the Partnership, and (vi) that the Units are offered and sold and
described in the Registration Statement, the Limited Partnership Agreement and
the Selling Agreement, the Units to be issued to the Subscribers will represent
valid limited partner interests in the Partnership and will be fully paid and
nonassessable limited partner interests in the Partnership, as to which the
Subscribers, as limited partners, will have no liability in excess of their
obligation to make payments provided for in the Limited Partnership Agreement
and their share of the Partnership's assets and undistributed profits (subject
to the obligation of a limited partner to repay any funds wrongfully distributed
to it).

     We hereby consent to use of our name under the heading "Legal Matters" in
the Prospectus forming a part of the Registration Statement and to use of this
opinion for filing as Exhibit 5.1 to the Registration Statement.

     This opinion is being furnished in accordance with the requirements of Item
601(b)(5) of Regulation S-K under the Act, in connection with the matters set
forth herein. Except as stated above, without our prior consent, this opinion
may not be furnished or quoted to, or relied upon by, any other person or entity
for any purpose.

Sincerely,


Mayer, Brown, Rowe & Maw LLP