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                                                              Exhibit 4
                                SECOND AMENDMENT
                                       TO
                                RIGHTS AGREEMENT

           SECOND AMENDMENT, dated as of August 20, 1995 (this "Second
Amendment"), to the Rights Agreement, dated as of June 17, 1986, between The
Upjohn Company, a Delaware corporation (the "Company"), and The Bank of New
York, as Rights Agent (the "Rights Agent"), as amended by the First Amendment
thereto, dated as of March 22, 1989, between the Company and the Rights Agent
(as so amended, the "Rights Agreement").

           Pursuant to Section 26 of the Rights Agreement, the Company and the
Rights Agent may, prior to the Distribution Date (as defined therein), amend any
provision of the Rights Agreement without the approval of any holders of
certificates representing the common stock of the Company. The Company now
desires to amend the Rights Agreement as set forth in this Second Amendment.
Pursuant to Section 26 of the Rights Agreement, the Company hereby directs that
the Rights Agreement should be amended as set forth in this Second Amendment.

           NOW THEREFORE, in consideration of the premises and the mutual
agreements herein set forth, the parties hereby agree as follows:

           1. Amendment of Section 1

           The Rights Agreement is hereby amended to delete in its entirety the
definition of "Acquiring Person" contained in subsection (a) of Section 1
thereof and to


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substitute the following definition of "Acquiring Person" therefor:

           "'Acquiring Person' shall mean any Person (as hereinafter defined)
           who or which, together with all Affiliates (as hereinafter defined)
           and Associates (as hereinafter defined) of such Person shall be the
           Beneficial Owner (as hereinafter defined) of 20% or more of the
           shares of Common Stock then outstanding, but shall not include (i)
           the Company, any Subsidiary of the Company, any employee benefit plan
           of the Company or any Subsidiary of the Company, any entity
           organized, appointed or established by the Company or any Subsidiary
           of the Company for or pursuant to the terms of any such plan or (ii)
           Pharmacia Aktiebolag, AB Volvo, Forvaltningsaktiebolaget Stattum or
           Bushwood, Bushwood Sub, or any of their respective Subsidiaries, but
           only with respect to and to the extent of shares of Common Stock
           acquired by such entities or their Affiliates in connection with the
           transactions contemplated by the Combination Agreement (as
           hereinafter defined)."

           The Rights Agreement is hereby further amended to delete in its
entirety the definition of "Stock Acquisition Date" contained in subsection (m)
of Section 1 thereof and to substitute the following definition of "Stock
Acquisition Date" therefor:

           "'Stock Acquisition Date' shall mean the first date on which the
           Company shall have publicly announced (by any means) that an
           Acquiring Person has become such."

           2. Additions to Section 1

           Section 1 of the Rights Agreement is hereby further amended to add
the following definitions:


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           "(c) 'Pharmacia' shall mean Pharmacia Aktiebolag, a corporation 
           organized under the laws of the Kingdom of Sweden.

           (e) 'Bushwood' shall mean Bushwood, Inc., a corporation organized
           under the laws of the State of Delaware.

           (f) 'Bushwood Sub' shall mean Bushwood Subsidiary, Inc., a
           corporation organized under the laws of the State of Delaware.

           (i) 'Combination Agreement' shall mean the Combination Agreement,
           dated as of August 20, 1995, among Pharmacia, the Company, Bushwood 
           and Bushwood Sub.

           (q) 'Stattum' shall mean Forvaltningsaktiebolaget Stattum, a 
           corporation organized under the laws of the Kingdom of Sweden.

           (u) 'Volvo' shall mean AB Volvo, a corporation organized under the
           laws of the Kingdom of Sweden."

           3. Revision of subsections of Section 1

           Subparagraphs (c), (d), (e), (f), (g), (h), (i), (j), (k), (l), (m),
(n), and (o) of Section 1 of the Rights Agreement are hereby relettered to
become subparagraphs (d), (g), (h), (j), (k), (l), (m), (n), (o), (p), (r), (s)
and (t) thereof, respectively.

           4. Amendment of Section 3(a)(i)

           Clause (i) of Section 3(a) of the Rights Agreement is hereby amended
by deleting the parenthetical phrase immediately after the phrase "tenth day"
and substituting in its place the following parenthetical phrase:

           "(or such later date after the Stock Acquisition Date as may be fixed
           by resolution of the Board of Directors of the Company)"


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           5. Amendment of Section 3(a)(ii)

           Clause (ii) of Section 3(a) of the Rights Agreement is hereby amended
by adding the following parenthetical phrase after the words "exchange offer":
"(except that the transactions contemplated by the Combination Agreement shall
not be considered a tender or exchange offer for purposes of this Rights
Agreement)." Clause (ii) of Section 3(a) of the Rights Agreement is further
amended by adding the words "resolution of" immediately after the words "may be
fixed by" in the parenthetical phrase immediately following the words "tenth
business day".

           6. Amendment to Section 3(c)

           The legend in Section 3(c) of the Rights Agreement is hereby amended
by adding the following clause immediately following the words "as amended as of
March 22, 1989":

           "and as of August 20, 1995."

           7. Amendment to Section 11(a)(ii)

           Clause (ii) of Section 11(a) of the Rights Agreement is hereby
amended by deleting the parenthetical phrase immediately after the phrase "tenth
day" and substituting in its place the following parenthetical phrase:

           "(or such later date as may be fixed by resolution of the Board of
           Directors of the Company)"

           8. Amendment to Section 23(a)(i)

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           Clause (a)(i) of Section 23 of the Rights Agreement is hereby amended
to delete in its entirety the parenthetical phrase following the phrase "tenth
day" and to substitute therefor the following parenthetical phrase:

           "(or such later date as may be fixed by resolution of the Board of
           Directors of the Company)"

           9. Amendment to Form of Rights Certificate

           The form of Right Certificate set forth in the Rights Agreement as
Exhibit B is hereby amended by amending and restating the second full paragraph
on page 3 thereof as follows:

           "Subject to the provisions of this Rights Agreement, the Rights
           evidenced by this Certificate may be, but are not required to be,
           redeemed by the Board of Directors at a redemption price of $0.05 per
           Right at any time prior to the close of business on the tenth day (or
           later date, as may be fixed by resolution of the Board of Directors
           of the Company) following the Stock Acquisition Date, as such term is
           defined in the Rights Agreement. At any time after any Person becomes
           an Acquiring Person, as such terms are defined in the Rights
           Agreement, the Rights evidenced by this Certificate may be, but are
           not required to be, exchanged by the Company for shares of Common
           Stock of the Company at an exchange ratio of three shares of Common
           Stock per Right. As provided in the Rights Agreement, the redemption
           price and the exchange ratio set forth above are the redemption price
           and exchange ratio as of June 17, 1986, March 22, 1989, and August
           20, 1995, respectively. As provided in the Rights Agreement, the
           redemption price and exchange ratio are subject to


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           modification and adjustment in certain events."

           10. Governing Law. This Second Amendment shall be deemed to be a
contract made under the laws of the State of Delaware and for all purposes shall
be governed by and construed in accordance with the laws of such state
applicable to contracts to be made and performed entirely within such state,
provided, however, that the rights and obligations of The Bank of New York, as
Rights Agent hereunder, shall be governed by the laws of the State of New York.

           11. Counterparts. This Second Amendment may be executed in any number
of counterparts, each of which shall for all purposes be deemed an original, and
all of which together shall constitute but one and the same instrument.

           Except as expressly set forth herein, this Second Amendment shall not
by implication or otherwise alter, modify, amend or in any way affect any of the
terms, conditions, obligations, covenants or agreements contained in the Rights
Agreement, all of which are ratified and

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affirmed in all respects and shall continue in full force and effect.


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           IN WITNESS WHEREOF, the parties hereto have caused this Second
Amendment to be duly executed as of the day and year first above written.

Attest                                        THE UPJOHN COMPANY

By: /s/  KENNETH M. CYRUS                     By: /s/  JOHN L. ZABRISKIE 
   ------------------------                      ---------------------------
   Name: Kenneth M. Cyrus                        Name: John L. Zabriskie
   Title: Executive Vice President,              Title: Chairman of the Board
          Secretary and General                         and Chief Executive
          Counsel                                       Officer


Attest                                        THE BANK OF NEW YORK

By: /s/ JOSEPHINE L. BISHOP                   By: /S/ JOHN I. SIVERTSEN
   ------------------------                      ---------------------------
   Name: Josephine L. Bishop                     Name: John I. Sivertsen
   Title: Assistant Vice President               Title: Vice President


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