SECURITIES AND EXCHANGE COMMISSION

                             WASHINGTON, D.C. 20549


                                   FORM 8-A/A
                                 AMENDMENT NO. 2

                FOR REGISTRATION OF CERTAIN CLASSES OF SECURITIES
                     PURSUANT TO SECTION 12(b) OR (g) OF THE
                         SECURITIES EXCHANGE ACT OF 1934

                                Monsanto Company
             (Exact name of registrant as specified in its charter)


        Delaware                                           43-0420020
(State of incorporation)                       (IRS Employer Identification No.)

                          800 North Lindbergh Boulevard
                            St. Louis, Missouri             63167
               (Address of principal executive offices)   (Zip Code)

If this form relates to the                       If this form relates to the
registration of a class of                        registration of a class of  
securities pursuant to Section                    securities pursuant to 
12(b) of the Exchange Act                         Section 12(g) of the Exchange
and is effective pursuant to                      Act and is effective pursuant
General Instruction A.(c),                        to General Instruction
please check the following                        box.   [  ]
box.   [X]        

        Securities to be registered pursuant to Section 12(b) of the Act:

     Title of each class                         Name of each exchange on which
     to be so registered                         each class is to be registered
- -------------------------------                 --------------------------------
Preferred Share Purchase Rights                      New York Stock Exchange

        Securities to be registered pursuant to Section 12(g) of the Act:

                                      NONE
                                (Title of Class)



                  The undersigned registrant hereby amends Items 1 and 2 of its
Registration Statement on Form 8-A (File No. 1-2516), filed with the Securities
and Exchange Commission on January 31, 1990, as amended by Amendment No. 1
thereto, filed with the Securities and Exchange Commission on August 3, 1998, as
set forth below.

Item 1.  DESCRIPTION OF REGISTRANT'S SECURITIES TO BE REGISTERED.

                  Monsanto Company (the "Company") and The First National Bank
of Boston (the "Rights Agent") entered into the Rights Agreement, dated January
26, 1990, between the Company and the Rights Agent (the "Rights Agreement"). On
June 5, 1996, the Company effected a five-for-one stock split in the form of a
400% stock distribution to stockholders of record on May 15, 1996 (the "1996
Stock Split"). On June 6, 1990, the Company effected a two-for-one stock split
in the form of a 100% stock distribution to stockholders of record on May 15,
1990 (the "1990 Stock Split"). The following description of the Company's
preferred share purchase rights (the "Rights") gives effect to the adjustments
resulting from the 1996 Stock Split and the 1990 Stock Split.

                  On January 26, 1990, the Board of Directors of the Company
declared a dividend of one Right for each outstanding share of Common Stock, par
value of $2 per share (the "Common Stock"), of the Company. The dividend was
paid on February 5, 1990 to the stockholders of record at the close of business
on February 5, 1990. Each Right entitles the registered holder to purchase from
the Company one one-thousandth of a share of Series A Junior Participating
Preferred Stock without par value (the "Preferred Stock"), of the Company at a
price of $45 per one one-thousandth of a share of Preferred Stock (the "Purchase
Price"), subject to adjustment. The description and terms of the Rights are set
forth in the Rights Agreement.

                  Until the earlier to occur of (i) the tenth day following a
public announcement that a person or group of affiliated or associated persons
(an "Acquiring Person") has acquired or obtained the right to acquire beneficial
ownership of 20% or more of the outstanding Common Stock or (ii) the tenth
business day (or such later date as may be determined by action of the Board of
Directors prior to such time as any person or group of affiliated persons
becomes an Acquiring Person) following the commencement of, or announcement of
an intention to make, a tender offer or exchange offer the consummation of which
would result in the beneficial ownership by a person or group of 20% or more of
the outstanding Common Stock (the earlier of such dates being called the
"Distribution Date"), the Rights will be evidenced, with respect to any of the
Common Stock certificates outstanding as of the close of business on February 5,
1990, by such Common Stock certificate with a copy of the Summary of Rights
attached thereto.

                  The Rights Agreement provides that, until the Distribution
Date (or earlier redemption or expiration of the Rights), the Rights will be
transferred with and only with the Common Stock. Until the Distribution Date (or
earlier redemption or expiration of the 




Rights), new Common Stock certificates issued after February 5, 1990 upon
transfer or new issuance of Common Stock will contain a notation incorporating
the Rights Agreement by reference. Until the Distribution Date (or earlier
redemption or expiration of the Rights), the surrender for transfer of any
certificates for Common Stock, outstanding as of the close of business on
February 5, 1990, even without such notation or a copy of the Summary of Rights
being attached thereto, will also constitute the transfer of the Rights
associated with the Common Stock represented by such certificate. As soon as
practicable following the Distribution Date, separate certificates evidencing
the Rights ("Right Certificates") will be mailed to holders of record of the
Common Stock as of the close of business on the Distribution Date and such
separate Right Certificates alone will evidence the Rights.

                  The Rights are not exercisable until the Distribution Date.
Pursuant to the Rights Agreement, the Rights will expire on February 5, 2000
(the "Final Expiration Date"), unless the Final Expiration Date is extended or
unless the Rights are earlier redeemed or exchanged by the Company, in each
case, as described below.

                  The Purchase Price payable, and the number of shares of
Preferred Stock or other securities or property issuable, upon exercise of the
Rights are subject to adjustment from time to time to prevent dilution (i) in
the event of a stock dividend on, or a subdivision, combination or
reclassification of, the Preferred Stock, (ii) upon the grant to holders of the
Preferred Stock of certain rights or warrants to subscribe for or purchase
Preferred Stock at a price, or securities convertible into Preferred Stock with
a conversion price, less than the then-current market price of the Preferred
Stock or (iii) upon the distribution to holders of the Preferred Stock of
evidences of indebtedness or assets (excluding regular periodic cash dividends
paid out of earnings or retained earnings or dividends payable in Preferred
Stock) or of subscription rights or warrants (other than those referred to
above).

                  The number of outstanding Rights and the number of one
one-thousandths of a share of Preferred Stock issuable upon exercise of each
Right are also subject to adjustment in the event of a stock split of the Common
Stock or a stock dividend on the Common Stock payable in Common Stock or
subdivisions, consolidations or combinations of the Common Stock occurring, in
any such case, prior to the Distribution Date.

                  Preferred Stock purchasable upon exercise of the Rights will
not be redeemable. Each share of Preferred Stock will be entitled to a minimum
preferential quarterly dividend payment of $1 per share but will be entitled to
an aggregate dividend of 1000 times the dividend declared per share of Common
Stock. In the event of liquidation, the holders of the Preferred Stock will be
entitled to a minimum preferential liquidation payment of $100 per share but
will be entitled to an aggregate payment of 1000 times the payment made per
share of Common Stock. Each share of Preferred Stock will have one vote, voting
together with the Common Stock. Finally, in the event of any merger,
consolidation or other transaction in which Common Stock is exchanged, each
share of Preferred Stock will be entitled to receive 

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1000 times the amount received per share of Common Stock. These rights are
protected by customary antidilution provisions.

                  Because of the nature of the Preferred Stock's dividend and
liquidation rights, the value of the one one-thousandth interest in a share of
Preferred Stock purchasable upon exercise of each Right should approximate the
value of one share of Common Stock.

                  In the event that the Company is acquired in a merger or other
business combination transaction or 50% or more of its consolidated assets or
earning power are sold, proper provision will be made so that each holder of a
Right will thereafter have the right to receive, upon the exercise thereof at
the then-current exercise price of the Right, that number of shares of common
stock of the acquiring company which at the time of such transaction will have a
market value of two times the exercise price of the Right. In the event that any
person or group of affiliated or associated persons becomes an Acquiring Person,
proper provision shall be made so that each holder of a Right, other than Rights
beneficially owned by the Acquiring Person (which will thereafter be void), will
thereafter have the right to receive upon exercise that number of shares of
Common Stock having a market value of two times the exercise price of the Right.

                  At any time after any Person becomes an Acquiring Person and
prior to the acquisition by such person or group of 50% or more of the
outstanding Common Stock, the Board of Directors of the Company may exchange the
Rights (other than Rights owned by such person or group which will have become
void), in whole or in part, at an exchange ratio of one share of Common Stock,
or one one-thousandth of a share of Preferred Stock (or of a share of a class or
series of the Company's preferred stock having equivalent rights, preferences
and privileges), per Right (subject to adjustment).

                  With certain exceptions, no adjustment in the Purchase Price
will be required until cumulative adjustments require an adjustment of at least
1% in such Purchase Price. No fractional shares of Preferred Stock will be
issued (other than fractions which are integral multiples of the number of one
one-thousandths of a share of Preferred Stock issuable upon the exercise of one
Right, which may, at the election of the Company, be evidenced by depositary
receipts) and in lieu thereof, an adjustment in cash will be made based on the
market price of the Preferred Stock on the last trading date prior to the date
of exercise.

                  At any time prior to the time that a person or group of
affiliated or associated persons has acquired beneficial ownership of 20% or
more of the outstanding Common Stock, the Company may redeem the Rights in
whole, but not in part, at a price of $.001 per Right (the "Redemption Price").
The redemption of the Rights may be made effective at such time on such basis
with such conditions as the Board of Directors of the Company in its sole
discretion may establish. Immediately upon any redemption of the Rights, the
right to exercise the Rights will terminate and the only right of the holders of
Rights will be to receive the Redemption Price.

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                  The terms of the Rights may be amended by the Board of
Directors of the Company without the consent of the holders of the Rights,
including an amendment to lower the 20% thresholds described above (including
the threshold for a person becoming an Acquiring Person) to not less than the
greater of (i) the sum of .001% and the largest percentage of the outstanding
Common Stock then known to the Company to be beneficially owned by any person or
group of affiliated or associated persons and (ii) 10%, except that from and
after such time as any person or group of affiliated or associated persons
becomes an Acquiring Person no such amendment may adversely affect the interests
of the holders of the Rights.

                  Until a Right is exercised, the holder thereof, as such, will
have no rights as a stockholder of the Company, including, without limitation,
the right to vote or to receive dividends.

                  The Rights have certain anti-takeover effects. The Rights will
cause substantial dilution to a person or group that attempts to acquire the
Company on terms not approved by the Company's Board of Directors, except
pursuant to an offer conditioned on a substantial number of Rights being
acquired. The Rights should not interfere with any merger or other business
combination approved by the Board of Directors since the Rights may be redeemed
by the Company at the Redemption Price prior to the time that a person or group
has acquired beneficial ownership of 20% or more of the Common Stock.

                  The Rights Agreement specifying the terms of the Rights and
including the form of the Certificate of Designations setting forth the terms of
the Preferred Stock as an exhibit thereto and the form of press release
announcing the declaration of the Rights are incorporated herein by reference.
The foregoing description of the Rights is qualified in its entirety by
reference to such exhibits.

                  On May 31, 1998, the Company entered into an Agreement and
Plan of Merger, dated as of May 31, 1998, among American Home Products
Corporation ("AHP"), MA Sub, Inc. ("Sub") and the Company (the "Merger
Agreement"), pursuant to which Sub would have been merged with and into the
Company (the "Merger"). In connection with the Merger Agreement, the Company and
First Chicago Trust Company of New York, as successor Rights Agent, entered into
the First Amendment (the "First Amendment"), dated as of May 31, 1998, to the
Rights Agreement. The First Amendment provided, among other things, that if the
Merger Agreement were to be terminated without the effective time of the Merger
having occurred, the First Amendment would be null and void.

                  On October 13, 1998, the Company, AHP and Sub terminated the
Merger Agreement without the effective time of the Merger having occurred,
thereby rendering the First Amendment null and void.

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Item 2.  EXHIBITS.

           1.   Rights Agreement, dated as of January 26, 1990, between Monsanto
                Company and First Chicago Trust Company of New York (as
                successor to The First National Bank of Boston), as Rights Agent
                (incorporated by reference to Monsanto Company's Registration
                Statement on Form 8-A filed with the Securities and Exchange
                Commission on January 31, 1990).

           2.   Press Release dated January 26, 1990 (incorporated by reference
                to Monsanto Company's Registration Statement on Form 8-A filed
                with the Securities and Exchange Commission on January 31,
                1990).











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                                    SIGNATURE

                  Pursuant to the requirements of Section 12 of the Securities
Exchange Act of 1934, the registrant has duly caused this registration statement
to be signed on its behalf by the undersigned, thereunto duly authorized.


Dated: October 20, 1998

                                            MONSANTO COMPANY

                                            By:  /s/ Hendrik A. Verfaillie
                                                  Name: Hendrik A. Verfaillie
                                                  Title:   President
















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                                  EXHIBIT LIST

No.
- ---

 1.      Rights Agreement, dated as of January 26, 1990, between Monsanto
         Company and First Chicago Trust Company of New York (as successor to
         The First National Bank of Boston), as Rights Agent (incorporated by
         reference to Monsanto Company's Registration Statement on Form 8-A
         filed with the Securities and Exchange Commission on January 31, 1990).

 2.      Press Release dated January 26, 1990 (incorporated by reference to
         Monsanto Company's Registration Statement on Form 8-A filed with the
         Securities and Exchange Commission on January 31, 1990).
















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