Exhibit 10(d)

AMENDMENT TO THE EMPLOYMENT AGREEMENT BETWEEN

SIGMA-ALDRICH CORPORATION AND JAI NAGARKATTI

WHEREAS, the Sigma-Aldrich Corporation (“Company”) and Jai Nagarkatti (“Chief
Executive Officer”) previously entered into an employment agreement
(“Agreement”) effective as of January 1, 2006; and

WHEREAS, the Company and Chief Executive Officer retained the right to amend the
Agreement in Section 3.10 thereof;

WHEREAS, the Plan has been administered in good faith compliance with
Section 409A of the Internal Revenue Code of 1986, as amended, and the
regulations and other guidance promulgated thereunder (“Code Section 409A”); and

WHEREAS, the Company and Chief Executive Officer desire to amend the Agreement,
effective December 31, 2008, to reflect documentary compliance with Code
Section 409A.

NOW, THEREFORE, in consideration of the foregoing, the Company and Chief
Executive Officer hereby agree to amend the Agreement, effective December 31,
2008, as follows:

1. Section 1.1(i) is deleted in its entirety and replaced with the following:

“(i) “Good Reason” when used with reference to a voluntary termination by
Executive from his employment with Company, shall mean (i) a material reduction
in Executive’s base salary as in effect on the date hereof, or as the same may
be increased from time to time, during the Employment Period; or (ii) a material
reduction in the Executive’s authorities, duties, or responsibilities during the
Employment Period; or notice of termination.”

2. Section 2.4(c)(iii) is deleted in its entirety and replaced with the
following:

“(iii) In the event that the Executive is determined to be a specified employee
in accordance with Section 409A of the Internal Revenue Code of 1986, as
amended, and the regulations and other guidance issued thereunder for purposes
of any severance pay payment under this subsection (c), such severance payments
shall begin on the first payroll date that is more than six months following the
date of separation from service, but only to the extent that such payments do
not satisfy either the short term deferral exception to Code Section 409A
described in 26 CFR §1.409A-1(b)(4) (“Short Term Deferral Exception”) or to the
extent such payments do not satisfy the Short Term Deferral Exception, the
involuntary termination exception to Code Section 409A described in 26 CFR
§1.409A-1(b)(9). At all times, the right to all such installment payments made
under this subsection (c) shall be treated as the right to a series of separate
payments within the meaning of 26 CFR §1.409A-2(b)(2)(iii).”

3. The last sentence of Section 2.4(d) is deleted in its entirety and replaced
with the following:

“Good Reason will only exist if the Executive provides the Company with written
notice of Good Reason within a period not to exceed 90 days after the initial
existence of the condition alleged to give rise to Good Reason, the Company
fails to remedy the condition within 30 days of such notice,

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and such Good Reason termination is within two years following the initial
existence of one or more conditions giving rise to Good Reason. In the event
that the Executive is determined to be a specified employee in accordance with
Section 409A of the Internal Revenue Code of 1986, as amended, and the
regulations and other guidance issued thereunder for purposes of any severance
pay payment under this subsection (c), such severance payments shall begin on
the first payroll date that is more than six months following the date of
separation from service, but only to the extent that such payments do not
satisfy either the short term deferral exception to Code Section 409A described
in 26 CFR §1.409A-1(b)(4) (“Short Term Deferral Exception”) or to the extent
such payments do not satisfy the Short Term Deferral Exception, the involuntary
termination exception to Code Section 409A described in 26 CFR §1.409A-1(b)(9).
At all times, the right to all such installment payments made under this
subsection (d) shall be treated as the right to a series of separate payments
within the meaning of 26 CFR §1.409A-2(b)(2)(iii).”

IN WITNESS WHEREOF, the parties hereto have executed this Amendment to the
Agreement this 30th day of December, 2008.

 

SIGMA-ALDRICH CORPORATION By:  

/s/ Richard A. Keffer

Name:   Richard A. Keffer Title:   Secretary Chief Executive Officer

/s/ Jai Nagarkatti

Jai Nagarkatti