Exhibit 5.1





                                                    Monsanto Company
                                                    800 N. Lindbergh Boulevard
                                                    St. Louis, Missouri 63167
                                                    Phone (314) 694-2819



                                December 5, 2000


Securities and Exchange Commission
450 Fifth Street, N.W.
Washington, DC 20549

Gentlemen:

As General  Counsel of  Monsanto  Company,  a  Delaware  Corporation  having its
general offices at 800 North Lindbergh Boulevard, St. Louis, Missouri 63167 (the
"Company"),  I am familiar  with the  Registration  Statement  on Form S-8 being
filed by the Company under the Securities  Act of 1933, as amended,  covering an
aggregate of 26,745,000 shares of Monsanto Company Common Stock, $0.01 par value
per share  ("Common  Stock"),  authorized  for delivery to certain  participants
under  the  Monsanto  2000  Management  Incentive  Plan,  the  Monsanto  Company
Non-Employee  Director Equity Incentive  Compensation Plan, the Monsanto Company
Broad-Based  Stock Option Plan and the Monsanto  Company Employee Stock Purchase
Plan (the "Plans").

I am also  familiar  with the  Company's  Amended and  Restated  Certificate  of
Incorporation  and its Amended and Restated  By-Laws as now in effect,  and with
all corporate and other  proceedings  taken by the Company's  Board of Directors
relative to the  authorization of the Plans,  including the proposed delivery of
up to an aggregate of 26,745,000 shares of Common Stock thereunder.

It is my opinion that the Company is a  corporation  duly  organized and validly
existing under the laws of the State of Delaware;  that the Plans, including the
proposed  delivery of up to an  aggregate of  26,745,000  shares of Common Stock
thereunder,  has been duly  authorized by  appropriate  corporate  action of the
Company;  and that  the  aforesaid  26,745,000  shares  of  Common  Stock,  when
delivered pursuant to the provisions of the Plans, will be legally issued, fully
paid and non-assessable.

I hereby  consent to the filing of this opinion as an exhibit to and  references
to this  opinion in said  Registration  Statement  and to its use in  connection
therewith.  My consent is not an  admission  that the  consent  is  required  by
Section 7 of the Securities Act of 1933.

                                        Very truly yours,

                                        /s/ R. William Ide III
                                        ----------------------

                                        R. William Ide III
                                        General Counsel, Monsanto Company