Exhibit 5.1


                  [Letterhead of Sonnenschein Nath & Rosenthal]


                                                     June 28, 2001

Monsanto Company
800 North Lindbergh Boulevard
St. Louis, Missouri 63167

         Re:      Registration Statement on Form S-8
                  Under the Securities Act of 1933

Ladies and Gentlemen:

     At your request,  we have examined the  Registration  Statement on Form S-8
being  filed   contemporaneously   herewith  by  Monsanto  Company,  a  Delaware
corporation  (the "Company"),  with the Securities and Exchange  Commission (the
"Registration Statement"), relating to the registration under the Securities Act
of 1933, as amended, of savings and investment plan obligations in the aggregate
principal amount of $24,000,000 (the  "Obligations")  under the Monsanto Company
ERISA Parity Savings and Investment Plan (the "Plan").

     We have examined the Plan and the corporate actions taken by the Company in
connection  with its adoption of the Plan and have assumed that the  Obligations
will be paid for by the Company in accordance with the terms of the Plan and the
resolutions authorizing their issue.

     In making the aforesaid  examinations,  we have assumed the genuineness and
authenticity of all documents  examined by us and all signatures therein and the
conformity to originals of all copies of all  documents  examined by us. We have
also assumed that the corporate  records  furnished to us by the Company include
all corporate proceedings taken by the Company to date.

     Based upon and subject to the  foregoing,  we are of the  opinion  that the
Obligations have been duly and validly authorized and, when issued in accordance
with  the  terms  of the  Plan,  will be  binding  obligations  of the  Company,
entitling the respective holders thereof to the benefits of the Plan.

     We  consent to the use of this  opinion  as an exhibit to the  Registration
Statement  and  further  consent  to all  references  to us in the  Registration
Statement,  the  prospectus  constituting  a part  thereof  and  any  amendments
thereto.  We do not,  by giving  such  consent,  admit  that we are  within  the
category of persons whose consent is required under Section 7 of the Act.

                                    Very truly yours,

                                    SONNENSCHEIN NATH & ROSENTHAL


                                    By:  /s/Ira I. Roxland
                                       -----------------------------------------
                                           A Member of the Firm