Document:

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                                                                  Exhibit 10 (l)
                                                                  --------------
                            FOURTH AMENDMENT TO THE
                            -----------------------
              SIGMA-ALDRICH CORPORATION SHARE OPTION PLAN OF 1995
              ---------------------------------------------------

     This Fourth Amendment to the Share Option Plan of 1995 is hereby approved
and adopted by Sigma-Aldrich Corporation (the "Company") effective as of the
November 22, 1999.

     WHEREAS, the Company established its Share Option Plan of 1995 (the "Plan")
to provide for the granting of options to purchase Common Stock of the Company
to certain key employees of the Company and its subsidiaries; and

     WHEREAS, the Company desires to amend the Plan to provide twelve months
rather than three months after (I) termination of employment by retirement or
(ii) termination of employment by the Company without cause for an optionee to
exercise the unexercised portion of an option provided that in no event shall
the original ten year termination date of such option be extended; and

     WHEREAS, the Plan provides that each option shall be exercisable in such
manner, at such time or times and subject to such conditions or limitations as
shall be fixed by the Compensation Committee of the Board (the "Committee"), in
its sole discretion at the time such option is granted; and

     WHEREAS, the Company desires to clarify that the Committee, in certain
circumstances, may amend the terms and conditions with respect to which an
option is exercisable after the time an option is granted.

     NOW, THEREFORE, the following amendments and modifications are hereby made
a part of the Plan:

    1.    Paragraph 8(b)(i) of the Plan is hereby amended and restated as
          follows:

(b) Termination of Employment After the Non-exercise Period
    -------------------------------------------------------

    (i)   By Retirement or Termination of Employment by the Company Without
          -----------------------------------------------------------------
          Cause
          -----
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     If the Non-exercise Period shall have elapsed and the optionee's employment
with the Company and every subsidiary of the Company shall have been terminated
by the Company thereafter without cause (as hereinafter defined) or shall
terminate because of the retirement of an optionee on a permitted Retirement
Date from the Company and all subsidiaries, the optionee shall have the right to
exercise the unexercised portion of the option at any time during a period of
twelve (12) months after the date of termination or retirement, in whole or in
part, to the extent the optionee could have exercised such option had he
remained in the employ of the Company during the twelve (12) month period. If a
subsidiary of the Company ceases to be a subsidiary of the Company, an optionee
who is employed by such former subsidiary and is no longer employed by either
the Company or any current subsidiary of the Company shall be deemed to have
terminated employment with the Company and every subsidiary of the Company and
such termination shall be deemed to have been made by the Company without cause.
The unexercised portion of the option shall terminate no later than twelve (12)
months after an optionee ceases to be an employee for any of the foregoing
reasons, and any unexercised portion shall terminate immediately if and when the
optionee becomes an employee, agent or principal of a competitor of the Company,
or of any subsidiary of the Company, without the consent of the Company.

     If an optionee dies within such twelve (12) month period at a time when the
optionee is not an employee, agent or principal of a competitor of the Company
or of any subsidiary (or when the Company has consented to such relationship
with a competitor), the option may be exercised at any time during the period of
twelve (12) months after the date of the death of the optionee by a designee,
for a number of Shares which the deceased optionee could have acquired by the
exercise of such option had the deceased optionee
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survived for the twelve (12) month, without regard to the requirement of
exercise within twelve (12) months after termination of employment.

     The Committee may, in its sole and absolute discretion, amend existing
options, which provide only three (3) months for exercise after termination by
retirement or termination by the Company without cause, to conform the
provisions of this Paragraph 8(b)(i) as amended.

     For purposes of this Plan, the term "designee" means the deceased
optionee's personal representative or any person who acquired the right to
exercise such option by bequest or inheritance or by reason of the laws of
descent and distribution. The term "Retirement Date" shall have the meaning set
forth in the Employees' Retirement Plan, as in effect from time to time, of the
optionee's employer, and shall include, where applicable, the Normal Retirement
Date, the Early Retirement Date, and Retirement By Reason of Disability as
defined in such Plan, or, if the optionee's employer has no such plan, the term
shall have the meaning set forth in the Federal Social Security Act, as in
effect from time to time.

IN WITNESS WHEREOF, the Company has executed this Fourth Amendment to the Share
Option Plan of 1995 as of the day and year first above written.

                                  SIGMA-ALDRICH CORPORATION

                              By: /s/ Michael R. Hogan
                                  --------------------
                                  Vice President<PAGE>

                                                                  Exhibit 10 (m)
                                                                  --------------
                            FIFTH AMENDMENT TO THE
                           SIGMA-ALDRICH CORPORATION
                           SHARE OPTION PLAN OF 1995

     This Fifth Amendment to the Sigma-Aldrich Corporation Share Option Plan of
1995 is hereby adopted by Sigma-Aldrich Corporation (the "Company") effective as
of February 20, 2001.

          WHEREAS, the Company established its Share Option Plan of 1995 (the
"Plan") to provide for the granting of options to purchase common stock of the
Company to certain key employees of the Company and its subsidiaries;

          WHEREAS, Paragraph 15 of the Plan provides that the Board of Directors
may make such amendments and modifications as it deems advisable, in its sole
discretion, subject to certain exceptions;

          WHEREAS, the Board of Directors desires to amend the Plan to provide
that options shall become vested and exercisable upon (i) termination of
employment by retirement or (ii) termination of employment by reason of death or
disability, subject to the terms and conditions of the Plan;  and

          WHEREAS, the Plan provides that each option shall be exercisable in
such manner, at such time or times and subject to such conditions or limitations
as shall be fixed by the Compensation Committee of the Board (the "Committee"),
in its sole discretion at the time such option is granted or after the time an
option is granted;

     1.   The first three sentences of Paragraph 6 are hereby deleted and
replaced with the following:

          "Except as provided in Paragraph 8, no option granted under this Plan
          may be exercised prior to the expiration of twelve (12) months from
          the date it is granted.  The Committee may specify a longer period of
          time during which an option may not be exercised at the time each
          option is granted.  Any period of non-exercise (whether shortened as
          provided in Paragraph 8 or lengthened as provided in the preceding
          sentence) is hereinafter referred to as the 'Non-exercise Period.'"

     2.   Paragraph 8(a) is hereby deleted and replaced with the following:

          "(a)  Termination of Employment During the Non-exercise Period
                --------------------------------------------------------

          "Except as provided in Paragraph 8(b) hereof, if, during the Non-
          exercise Period, the optionee's employment with the Company and every
          subsidiary of the Company shall terminate for any reason, the
          optionee's right to exercise the option shall terminate and all rights
          thereunder shall cease."

     3.   The first three paragraphs of Paragraph 8(b)(i) are hereby deleted and
replaced with the following:
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          "If the Non-exercise Period shall have elapsed and the optionee's
          employment with the Company and every subsidiary of the Company shall
          have been terminated by the Company thereafter without cause (as
          hereinafter defined) or shall terminate because of the retirement of
          an optionee on a permitted Retirement Date from the Company and all
          subsidiaries, the optionee shall have the right to exercise the
          unexercised portion of the option at any time during a period of
          twelve (12) months after the date of termination or retirement, in
          whole or in part, (x) in the case of  termination of the optionee's
          employment by the Company without cause, to the extent the optionee
          could have exercised such option had the optionee remained in the
          employ of the Company during the twelve (12) month period or (y) in
          the case of termination because of retirement of an optionee on a
          permitted Retirement Date, to the extent of any or all the options
          held by the optionee, whether or not the Non-exercise Period shall
          have elapsed with respect to such options.  If a subsidiary of the
          Company ceases to be a subsidiary of the Company, an optionee who is
          employed by such former subsidiary and is no longer employed by either
          the Company or any current subsidiary of the Company shall be deemed
          to have terminated employment with the Company and every subsidiary of
          the Company and such termination shall be deemed to have been made by
          the Company without cause.  The unexercised portion of the option
          shall terminate no later than twelve (12) months after an optionee
          ceases to be an employee for any of the foregoing reasons, and any
          unexercised portion shall terminate immediately if and when the
          optionee becomes an employee, agent or principal of a competitor of
          the Company, or of any subsidiary of the Company, without the consent
          of the Company.

          "If an optionee dies within such twelve (12) month period at a time
          when the optionee is not an employee, agent or principal of a
          competitor of the Company or of any subsidiary (or when the Company
          has consented to such relationship with a competitor), the option may
          be exercised at any time during the period of twelve (12) months after
          the date of the death of the optionee by a designee, (x) in the case
          of termination of the optionee's employment by the Company without
          cause, for the number of shares which the deceased optionee could have
          acquired by the exercise of such option had the deceased optionee
          survived for the twelve (12) month period, without regard to the
          requirement of exercise within twelve (12) months after termination of
          employment or (y) in the case of termination because of retirement of
          an optionee on a permitted Retirement Date, for the number of shares
          subject to any or all the options held by the deceased optionee,
          whether or not the Non-exercise Period shall have elapsed with respect
          to such options, without regard to the requirement of exercise within
          twelve (12) months after termination of employment.

          "The Committee may, in its sole and absolute discretion, amend
          existing options to conform to the provisions of this Paragraph
          8(b)(i) as amended."
<PAGE>

     4.   Paragraph 8(b)(ii) is hereby deleted and replaced with the following:

          "(ii)  By Death or Permanent and Total Disability
                 ------------------------------------------

          "If an optionee dies or is totally and permanently disabled (within
          the meaning of Section 22(e)(3) of the Internal Revenue Code) while in
          the employ of the Company or any subsidiary, the option may be
          exercised by the optionee or by the optionee's personal representative
          at any time during the twelve (12) month period after the date of such
          death or disability for the total number of shares subject to such
          person's options, whether or not the Non-exercise Period shall have
          elapsed with respect to such options."

     5.   In all other respects, the Plan, as amended, is hereby ratified and
confirmed.

          IN WITNESS WHEREOF, the Company has executed this Fifth Amendment to
the Share Option Plan of 1995 as of the day and year first above written.

                                   SIGMA-ALDRICH CORPORATION

                                   By /s/ David R. Harvey
                                      -------------------
                                      President

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