SIGMA ALDRICH CORP
FOURTH AMENDMENT TO SHARE OPTION PLAN 1995
<DOCUMENT>
<TYPE>EX-10.(L)
<SEQUENCE>8
<FILENAME>0008.txt
<DESCRIPTION>FOURTH AMENDMENT TO SHARE OPTION PLAN 1995
<TEXT>

<PAGE>

                                                                  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
          -----
<PAGE>

     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
<PAGE>

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
</TEXT>
</DOCUMENT>
