As Filed with the Securitites and Exchange Commision on September 29, 1998
                                                      Registration No._______
________________________________________________________________________________

                      SECURITIES AND EXCHANGE COMMISSION
                           Washington, D.C. 20549
              _______________________________________________________
                                   FORM S-8
              REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933
              _______________________________________________________

                           SIGMA-ALDRICH CORPORATION
              (Exact Name Of Registrant As Specified In Its Charter)
  Delaware                                                   43-1050617
(State or other jurisdiction of                           (I.R.S. Employer
 incorporation or organization)                           Identification No.)
                                  3050 Spruce Street
                               St. Louis, Missouri 63103
                                    (314) 771-5765
                      (Address, including zip code, and telephone number,
                      including area code of, registrant's principal
                      executive office)
               ------------------------------------------------------ 
                        SIGMA-ALDRICH CORPORATION DIRECTORS'
                        NONQUALIFIED SHARE OPTION PLAN OF 1998
                               (Full Title of the Plan)

                                   KIRK A. RICHTER
                                      Treasurer
                              Sigma-Aldrich Corporation
                                 3050 Spruce Street
                                St. Louis, MO  63103
                                  (314) 771-5765
                (Name, Address, including Zip Code and Telephone Number,
                including Area Code, of Agent For Service)

                          Copies of all correspondence to:
                                R. Randall Wang, Esq.
                                   Bryan Cave LLP
                             211 N. Broadway, Suite 3600
                                St. Louis, MO  63102
                                   (314) 259-2000

                           CALCULATION OF REGISTRATION FEE

Title of                                 Proposed     Proposed  
each class                               maximum      maximum
securities            Amount             offering     aggregate   Amount of
to be                 to be              price per    offering    registration
registered            registered         unit(2)      price(2)    fee

Common Stock, $1.00
par value per share   400,000shares(1)   31.7369      12,694,760  3745.00
                       


(1)  The registration statement also includes an indeterminable number
     of additional shares that may become issuable pursuant to
     antidilution provisions.

(2)  Estimated solely for the purpose of calculating the registration
     fee pursuant to Rule 457(c) and Rule 457(h) based on (i) the
     weighted average price per share based on the exercise price of
     stock options already granted and (ii) on the average of the high
     and low prices for the Common Stock on September 22, 1998, as
     reported on The Nasdaq National Market with respect to securities
     for which options have not been granted.

                                    PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3.   Incorporation of Documents by Reference.

     The following documents, which are on file with the Securities
and Exchange Commission, are incorporated herein by reference:

          (a) Sigma-Aldrich Corporation's ("Sigma-Aldrich" or the
     "Company") Annual Report on Form 10-K for the year ended
     December 31, 1997 (File No. 0-8135);

          (b) The Company's Quarterly Reports on Form 10-Q for the
     quarters ended March 31, 1998 and June 30, 1998 (File No. 0-8135);

          (c) The description of the Company's Common Stock
     contained in the Company's registration statement on Form S-14
     under the Securities Act of 1933, dated May 16, 1975 (File No.
     2-53698), as amended by the description contained in the
     Company's proxy statements dated May 29, 1984 under the
     caption "Proposal to amend Certificate of Incorporation,"
     dated March 29, 1991 under the caption "Proposal to amend
     Certificate of Incorporation to Increase authorized Common
     Stock" and dated March 29, 1996 under the caption "Proposal to
     Amend Certificate of Incorporation to Increase Number of
     Shares of Authorized Common Stock."

     All documents subsequently filed by Sigma-Aldrich pursuant to
Sections 13(a), 13(c), 14, and 15(d) of the Securities Exchange Act
of 1934, prior to the filing of a post-effective amendment which
indicates that all securities offered have been sold or which
deregisters all securities then remaining unsold, shall be deemed
to be incorporated by reference and to be a part hereof from the
date of filing of such documents.  Any statement contained herein
or in a document incorporated, or deemed to be incorporated, by
reference herein, shall be deemed to be modified or superseded for
purposes hereof to the extent that a statement contained herein or
in any other subsequently filed document which also is or is deemed
to be incorporated by reference herein modifies or supersedes such
statement.  Any such statement so modified or superseded shall not
be deemed, except as so modified or superseded, to constitute a
part hereof.

Item 4. Description of Securities.

     The authorized capital stock of the Company consists of
200,000,000 shares of Common Stock, $1.00 par value per share.
Dividends may be paid on the Common Stock as and when declared by
the Board of Directors out of any funds legally available therefor.
The holders of Common Stock are entitled to one vote per share in
the election of directors and in respect of other matters submitted
to shareholders for a vote.  Upon liquidation, the holders of the
Common Stock are entitled to receive all assets of the Company
available for distribution to shareholders pro rata in accordance
with their holdings.

     The Company's Certificate of Incorporation as amended requires
that a merger or consolidation of the Company with another
corporation or which involves a subsidiary of the Company when
shares of the Company in excess of 35 percent of the outstanding
shares are issued; a sale of assets having an aggregate book value
of 20 percent of the Company's total assets; the adoption of a plan
of liquidation or dissolution; and certain related transactions,
must be approved by the affirmative vote of two-thirds of the
shares of voting stock.

     The Common Stock has no preemptive or conversion rights,
redemption provisions or sinking fund provisions.  The outstanding
Common Stock, including the Common Stock offered hereby, is fully-
paid and nonassessable.

Item 5. Interests of Named Experts and Counsel.

     Jerome W. Sandweiss, a Director of the Company, is of counsel
with the law firm of Blumenfeld, Kaplan & Sandweiss, P.C.  Mr.
Sandweiss owns, directly and indirectly, an aggregate of Fourteen
Thousand (14,000) shares of the Company's Common Stock plus options
to acquire Twelve Thousand (12,000) shares of the Company's Common
Stock.  Blumenfeld, Kaplan & Sandweiss, P.C. has rendered its
opinion concerning the shares of Common Stock covered by the Plan
as set forth in Exhibit No. 5 to this registration statement.

Item 6. Indemnification of Directors and Officers.

     Section 145(a) of the Delaware General Corporation Law
provides that a corporation may indemnify any director, officer,
employee or agent of the corporation in any action, other than an
action by or in the right of the corporation, if such person acted
in good faith and in a manner he reasonably believed to be in or
not opposed to the best interests of the corporation and, with
respect to any criminal action, had no reasonable cause to believe
his conduct was unlawful.  Section 145(b) provides that the
corporation may indemnify any such person in an action by or in the
right of the corporation if he acted in good faith and in a manner
he reasonably believed to be in or not opposed to the best
interests of the corporation, except that such person may not be
indemnified in respect of any matter in which he has been judged
liable to the corporation, unless authorized by the court.  Section
145(c) provides that the corporation shall indemnify any such
person against expenses actually and reasonably incurred in defense
of any action if he has been successful in defense of such action
and if such action is one for which the corporation may indemnify
such person under Section 145(a) or (b).

     The Company's By-Laws provide that it shall indemnify, and in
the Company's discretion may obtain insurance for the benefit of
its officers and directors, to the extent permitted by applicable
Delaware law.

     Pursuant to amendments of the Delaware General Corporation Law
effective July 1, 1986, the Company's Certificate of Incorporation
eliminates the personal liability of directors to the Company or
its shareholders for monetary damages for breach of fiduciary duty
as a director, except (i) for breaches of the duty of loyalty to
the Company or its shareholders, (ii) for acts or omissions not in
good faith or involving intentional misconduct or knowing violation
of law, (iii) for the payment of unlawful dividends or unlawful
stock repurchases or redemptions, or (iv) for transactions in which
the director received an improper personal benefit.

Item 7. Exemption from Registration Claimed.

     Not applicable.

Item 8. Exhibits.

     See Exhibit Index.

Item 9. Undertakings.

          (a) The undersigned registrant hereby undertakes:

               (1) To file, during any period in which offers or sales are
     being made, a post-effective amendment to this registration statement:

                    (i)  To include any prospectus required by
          Section 10(a)(3) of the Securities Act of 1933;

                    (ii)  To reflect in the prospectus any facts or
          events arising after the effective date of the
          registration statement (or the most recent post-effective
          amendment thereof) which, individually or in the
          aggregate represent a fundamental change in the
          information set forth in the registration statement.
          Notwithstanding the foregoing, any increase or decrease
          in volume of securities offered (if the total dollar
          value of securities offered would not exceed that which
          was registered) and any deviation from the low or high
          end of the estimated maximum offering range may be
          reflected in the form of prospectus filed with the
          Commission pursuant to Rule 424(b) if, in the aggregate,
          the changes in volume and price represent no more than a
          20 percent change in the maximum aggregate offering price
          set forth in the "Calculation of Registration Fee" table
          in the effective registration statement;

                    (iii) To include any material information with
          respect to the plan of distribution not previously
          disclosed in the registration statement or any material
          change to such information in the registration statement;
          provided, however, that paragraphs (a)(1)(i) and (a)(1)(ii) do
          not apply if the registration statement is on Form S-3, Form S-8, 
          or Form F-3, and the information required to be included in
          a post-effective amendment by those paragraphs is contained in
          periodic reports filed with or furnished to the Commission by
          the Registrant pursuant to Section 13 or Section 15(d) of the
          Securities Exchange Act of 1934 that are incorporated by
          reference in the registration statement.

               (2) That, for the purpose of determining any
          liability under the Securities Act of 1933, each such post-
          effective amendment shall be deemed to be a new registration
          statement relating to the securities offered therein, and the
          offering of such securities at that time shall be deemed to be
          the initial bona fide offering thereof.

               (3) To remove from registration by means of a post-
          effective amendment any of the securities being registered
          which remain unsold at the termination of the offering.

          (b)  The undersigned Registrant hereby undertakes that,
          for purposes of determining any liability under the Securities
          Act of 1933, each filing of the Registrant's annual report
          pursuant to Section 13(a) or 15(d) of the Securities Exchange
          Act of 1934 (and, where applicable, each filing of an employee
          benefit plan's annual report pursuant to Section 15(d) of the
          Securities Exchange Act of 1934) that is incorporated by
          reference in the registration statement shall be deemed to be
          a new registration statement relating to the securities
          offered therein, and the offering of such securities at that
          time shall be deemed to be the initial bona fide offering
          thereof.

          (c)  Insofar as indemnification for liabilities arising
          under the Securities Act of 1933 may be permitted to
          directors, officers, and controlling persons of the Registrant
          pursuant to the foregoing provisions, or otherwise, the
          Registrant has been advised that in the opinion of the
          Securities and Exchange Commission such indemnification is
          against public policy as expressed in the Act and is,
          therefore, unenforceable.  In the event that a claim for
          indemnification against such liabilities (other than the
          payment by the Registrant of expenses incurred or paid by a
          director, officer, or controlling person of the Registrant in
          the successful defense of any action, suit, or proceeding) is
          asserted by such director, officer, or controlling person in
          connection with the securities being registered, the
          Registrant will, unless in the opinion of its counsel the
          matter has been settled by controlling precedent, submit to a
          court of appropriate jurisdiction the question whether such
          indemnification by it is against public policy as expressed in
          the Act and will be governed by the final adjudication of such
          issue.

                                  SIGNATURES

     Pursuant to the requirements of the Securities Act of 1933,
the Registrant certifies that it has reasonable grounds to believe
that it meets all of the requirements for filing on Form S-8 and
has duly caused this registration statement to be signed on its
behalf by the undersigned, thereunto duly authorized in the City of
St. Louis and State of Missouri on the 28th day of September, 1998.

                                                SIGMA-ALDRICH CORPORATION
                                   
                                   
                                                By:  /S/Kirk A. Richter
                                   
                                                Kirk A. Richter, Treasurer
                                   
                             POWER OF ATTORNEY

     Each person whose signature appears below constitutes and
appoints Karen J. Miller, Thomas M. Tallarico and Kirk A. Richter,
and either of them, his or her true and lawful attorneys-in-fact
and agents, with full power of substitution and resubstitution, for
him or her and in his or her name, place and stead, in any and all
capacities, to sign any or all amendments to this registration
statement and to file the same, with all exhibits thereto and all
other documents in connection therewith with the Securities and
Exchange Commission, granting unto said attorneys-in-fact and
agents full power and authority to do and perform each and every
act and thing requisite and necessary to be done in and about the
premises, as fully as he or she might or could do in person, hereby
ratifying and confirming all that said attorneys-in-fact and agents
may lawfully do or cause to be done by virtue hereof.

     Pursuant to the requirements of the Securities Act of 1933,
this registration statement has been signed below by the following
persons on behalf of the Registrant and in the capacities and on
the dates indicated.

       Signature                     Title


/S/Carl T. Cori            Director, Chairman of the Board   September 28, 1998
   Carl T. Cori            and Chief Executive Officer                Date


/S/David R. Harvey        Director, President and            September 28, 1998
   David R. Harvey        Chief Operating Officer                     Date


/S/Karen J. Miller        Controller                         September 28, 1998
   Karen J. Miller                                                    Date


/S/Kirk A. Richter         Treasurer                         September 28, 1998
   Kirk A. Richter                                                    Date


/S/Thomas M. Tallarico     Vice President and Secretary      September 28, 1998
   Thomas M. Tallarico                                                Date


/S/David M. Kipnis         Director                          September 28, 1998
   David M. Kipnis                                                     Date


/S/Andrew E. Newman         Director                         September 28, 1998
   Andrew E. Newman                                                    Date


/S/Jerome W. Sandweiss      Director                         September 28, 1998
  Jerome W. Sandweiss                                                  Date


                                     EXHIBIT INDEX

Exhibit Number      Description
--------------      -----------
     
     4.1            Certificate of Incorporation, as
                    amended (incorporated by reference
                    to Exhibit 3(a) of Form 10-Q for
                    the quarter ended September 30,
                    1996, File No. 0-8135)
     
     4.2            By-Laws, as amended (incorporated
                    by reference to Exhibit 3(b) of
                    Form 10-K filed for year ended
                    December 31, 1997, File No. 0-8135)
     
     5.1            Opinion of Counsel
     
     10.1           Sigma-Aldrich Corporation
                    Directors' Nonqualified
                    Share Option Plan of 1998
                    (incorporated by reference to
                    Appendix A to the definitive Proxy
                    Statement dated March 27, 1998 for
                    the Company's Annual Meeting of
                    Shareholders held on May 5, 1998,
                    File No. 0-8135).
     
     23.1           Consent of Counsel (included in
                    Exhibit 5.1)
     
     23.2           Consent of Arthur Andersen LLP
     
     24.1           Power of Attorney (included on
                    signature page)
[{"type": "S-8", "sequence": "1", "secsgml_size_bytes": 19485}]
{"company-data": {"conformed-name": "SIGMA ALDRICH CORP", "cik": "0000090185", "assigned-sic": "5160", "irs-number": "431050617", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-64661", "film-number": "98717662"}, "business-address": {"street1": "3050 SPRUCE ST", "city": "ST LOUIS", "state": "MO", "zip": "63103", "phone": "3147715765"}, "mail-address": {"street1": "3050 SPRUCE STREET", "city": "ST LOUIS", "state": "MO", "zip": "63103"}, "former-company": [{"former-conformed-name": "SIGMA INTERNATIONAL LTD", "date-changed": "19750925"}, {"former-conformed-name": "ALDRICH CHEMICAL CO INC", "date-changed": "19750908"}]}
As Filed with the Securitites and Exchange Commision on September 29, 1998
                                                      Registration No._______
________________________________________________________________________________

                      SECURITIES AND EXCHANGE COMMISSION
                           Washington, D.C. 20549
              _______________________________________________________
                                   FORM S-8
              REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933
              _______________________________________________________

                           SIGMA-ALDRICH CORPORATION
              (Exact Name Of Registrant As Specified In Its Charter)
  Delaware                                                   43-1050617
(State or other jurisdiction of                           (I.R.S. Employer
 incorporation or organization)                           Identification No.)
                                  3050 Spruce Street
                               St. Louis, Missouri 63103
                                    (314) 771-5765
                      (Address, including zip code, and telephone number,
                      including area code of, registrant's principal
                      executive office)
               ------------------------------------------------------ 
                        SIGMA-ALDRICH CORPORATION DIRECTORS'
                        NONQUALIFIED SHARE OPTION PLAN OF 1998
                               (Full Title of the Plan)

                                   KIRK A. RICHTER
                                      Treasurer
                              Sigma-Aldrich Corporation
                                 3050 Spruce Street
                                St. Louis, MO  63103
                                  (314) 771-5765
                (Name, Address, including Zip Code and Telephone Number,
                including Area Code, of Agent For Service)

                          Copies of all correspondence to:
                                R. Randall Wang, Esq.
                                   Bryan Cave LLP
                             211 N. Broadway, Suite 3600
                                St. Louis, MO  63102
                                   (314) 259-2000

                           CALCULATION OF REGISTRATION FEE

Title of                                 Proposed     Proposed  
each class                               maximum      maximum
securities            Amount             offering     aggregate   Amount of
to be                 to be              price per    offering    registration
registered            registered         unit(2)      price(2)    fee

Common Stock, $1.00
par value per share   400,000shares(1)   31.7369      12,694,760  3745.00
                       

(1)  The registration statement also includes an indeterminable number
     of additional shares that may become issuable pursuant to
     antidilution provisions.

(2)  Estimated solely for the purpose of calculating the registration
     fee pursuant to Rule 457(c) and Rule 457(h) based on (i) the
     weighted average price per share based on the exercise price of
     stock options already granted and (ii) on the average of the high
     and low prices for the Common Stock on September 22, 1998, as
     reported on The Nasdaq National Market with respect to securities
     for which options have not been granted.

                                    PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3.   Incorporation of Documents by Reference.

     The following documents, which are on file with the Securities
and Exchange Commission, are incorporated herein by reference:

          (a) Sigma-Aldrich Corporation's ("Sigma-Aldrich" or the
     "Company") Annual Report on Form 10-K for the year ended
     December 31, 1997 (File No. 0-8135);

          (b) The Company's Quarterly Reports on Form 10-Q for the
     quarters ended March 31, 1998 and June 30, 1998 (File No. 0-8135);

          (c) The description of the Company's Common Stock
     contained in the Company's registration statement on Form S-14
     under the Securities Act of 1933, dated May 16, 1975 (File No.
     2-53698), as amended by the description contained in the
     Company's proxy statements dated May 29, 1984 under the
     caption "Proposal to amend Certificate of Incorporation,"
     dated March 29, 1991 under the caption "Proposal to amend
     Certificate of Incorporation to Increase authorized Common
     Stock" and dated March 29, 1996 under the caption "Proposal to
     Amend Certificate of Incorporation to Increase Number of
     Shares of Authorized Common Stock."

     All documents subsequently filed by Sigma-Aldrich pursuant to
Sections 13(a), 13(c), 14, and 15(d) of the Securities Exchange Act
of 1934, prior to the filing of a post-effective amendment which
indicates that all securities offered have been sold or which
deregisters all securities then remaining unsold, shall be deemed
to be incorporated by reference and to be a part hereof from the
date of filing of such documents.  Any statement contained herein
or in a document incorporated, or deemed to be incorporated, by
reference herein, shall be deemed to be modified or superseded for
purposes hereof to the extent that a statement contained herein or
in any other subsequently filed document which also is or is deemed
to be incorporated by reference herein modifies or supersedes such
statement.  Any such statement so modified or superseded shall not
be deemed, except as so modified or superseded, to constitute a
part hereof.

Item 4. Description of Securities.

     The authorized capital stock of the Company consists of
200,000,000 shares of Common Stock, $1.00 par value per share.
Dividends may be paid on the Common Stock as and when declared by
the Board of Directors out of any funds legally available therefor.
The holders of Common Stock are entitled to one vote per share in
the election of directors and in respect of other matters submitted
to shareholders for a vote.  Upon liquidation, the holders of the
Common Stock are entitled to receive all assets of the Company
available for distribution to shareholders pro rata in accordance
with their holdings.

     The Company's Certificate of Incorporation as amended requires
that a merger or consolidation of the Company with another
corporation or which involves a subsidiary of the Company when
shares of the Company in excess of 35 percent of the outstanding
shares are issued; a sale of assets having an aggregate book value
of 20 percent of the Company's total assets; the adoption of a plan
of liquidation or dissolution; and certain related transactions,
must be approved by the affirmative vote of two-thirds of the
shares of voting stock.

     The Common Stock has no preemptive or conversion rights,
redemption provisions or sinking fund provisions.  The outstanding
Common Stock, including the Common Stock offered hereby, is fully-
paid and nonassessable.

Item 5. Interests of Named Experts and Counsel.

     Jerome W. Sandweiss, a Director of the Company, is of counsel
with the law firm of Blumenfeld, Kaplan & Sandweiss, P.C.  Mr.
Sandweiss owns, directly and indirectly, an aggregate of Fourteen
Thousand (14,000) shares of the Company's Common Stock plus options
to acquire Twelve Thousand (12,000) shares of the Company's Common
Stock.  Blumenfeld, Kaplan & Sandweiss, P.C. has rendered its
opinion concerning the shares of Common Stock covered by the Plan
as set forth in Exhibit No. 5 to this registration statement.

Item 6. Indemnification of Directors and Officers.

     Section 145(a) of the Delaware General Corporation Law
provides that a corporation may indemnify any director, officer,
employee or agent of the corporation in any action, other than an
action by or in the right of the corporation, if such person acted
in good faith and in a manner he reasonably believed to be in or
not opposed to the best interests of the corporation and, with
respect to any criminal action, had no reasonable cause to believe
his conduct was unlawful.  Section 145(b) provides that the
corporation may indemnify any such person in an action by or in the
right of the corporation if he acted in good faith and in a manner
he reasonably believed to be in or not opposed to the best
interests of the corporation, except that such person may not be
indemnified in respect of any matter in which he has been judged
liable to the corporation, unless authorized by the court.  Section
145(c) provides that the corporation shall indemnify any such
person against expenses actually and reasonably incurred in defense
of any action if he has been successful in defense of such action
and if such action is one for which the corporation may indemnify
such person under Section 145(a) or (b).

     The Company's By-Laws provide that it shall indemnify, and in
the Company's discretion may obtain insurance for the benefit of
its officers and directors, to the extent permitted by applicable
Delaware law.

     Pursuant to amendments of the Delaware General Corporation Law
effective July 1, 1986, the Company's Certificate of Incorporation
eliminates the personal liability of directors to the Company or
its shareholders for monetary damages for breach of fiduciary duty
as a director, except (i) for breaches of the duty of loyalty to
the Company or its shareholders, (ii) for acts or omissions not in
good faith or involving intentional misconduct or knowing violation
of law, (iii) for the payment of unlawful dividends or unlawful
stock repurchases or redemptions, or (iv) for transactions in which
the director received an improper personal benefit.

Item 7. Exemption from Registration Claimed.

     Not applicable.

Item 8. Exhibits.

     See Exhibit Index.

Item 9. Undertakings.

          (a) The undersigned registrant hereby undertakes:

               (1) To file, during any period in which offers or sales are
     being made, a post-effective amendment to this registration statement:

                    (i)  To include any prospectus required by
          Section 10(a)(3) of the Securities Act of 1933;

                    (ii)  To reflect in the prospectus any facts or
          events arising after the effective date of the
          registration statement (or the most recent post-effective
          amendment thereof) which, individually or in the
          aggregate represent a fundamental change in the
          information set forth in the registration statement.
          Notwithstanding the foregoing, any increase or decrease
          in volume of securities offered (if the total dollar
          value of securities offered would not exceed that which
          was registered) and any deviation from the low or high
          end of the estimated maximum offering range may be
          reflected in the form of prospectus filed with the
          Commission pursuant to Rule 424(b) if, in the aggregate,
          the changes in volume and price represent no more than a
          20 percent change in the maximum aggregate offering price
          set forth in the "Calculation of Registration Fee" table
          in the effective registration statement;

                    (iii) To include any material information with
          respect to the plan of distribution not previously
          disclosed in the registration statement or any material
          change to such information in the registration statement;
          provided, however, that paragraphs (a)(1)(i) and (a)(1)(ii) do
          not apply if the registration statement is on Form S-3, Form S-8, 
          or Form F-3, and the information required to be included in
          a post-effective amendment by those paragraphs is contained in
          periodic reports filed with or furnished to the Commission by
          the Registrant pursuant to Section 13 or Section 15(d) of the
          Securities Exchange Act of 1934 that are incorporated by
          reference in the registration statement.

               (2) That, for the purpose of determining any
          liability under the Securities Act of 1933, each such post-
          effective amendment shall be deemed to be a new registration
          statement relating to the securities offered therein, and the
          offering of such securities at that time shall be deemed to be
          the initial bona fide offering thereof.

               (3) To remove from registration by means of a post-
          effective amendment any of the securities being registered
          which remain unsold at the termination of the offering.

          (b)  The undersigned Registrant hereby undertakes that,
          for purposes of determining any liability under the Securities
          Act of 1933, each filing of the Registrant's annual report
          pursuant to Section 13(a) or 15(d) of the Securities Exchange
          Act of 1934 (and, where applicable, each filing of an employee
          benefit plan's annual report pursuant to Section 15(d) of the
          Securities Exchange Act of 1934) that is incorporated by
          reference in the registration statement shall be deemed to be
          a new registration statement relating to the securities
          offered therein, and the offering of such securities at that
          time shall be deemed to be the initial bona fide offering
          thereof.

          (c)  Insofar as indemnification for liabilities arising
          under the Securities Act of 1933 may be permitted to
          directors, officers, and controlling persons of the Registrant
          pursuant to the foregoing provisions, or otherwise, the
          Registrant has been advised that in the opinion of the
          Securities and Exchange Commission such indemnification is
          against public policy as expressed in the Act and is,
          therefore, unenforceable.  In the event that a claim for
          indemnification against such liabilities (other than the
          payment by the Registrant of expenses incurred or paid by a
          director, officer, or controlling person of the Registrant in
          the successful defense of any action, suit, or proceeding) is
          asserted by such director, officer, or controlling person in
          connection with the securities being registered, the
          Registrant will, unless in the opinion of its counsel the
          matter has been settled by controlling precedent, submit to a
          court of appropriate jurisdiction the question whether such
          indemnification by it is against public policy as expressed in
          the Act and will be governed by the final adjudication of such
          issue.

                                  SIGNATURES

     Pursuant to the requirements of the Securities Act of 1933,
the Registrant certifies that it has reasonable grounds to believe
that it meets all of the requirements for filing on Form S-8 and
has duly caused this registration statement to be signed on its
behalf by the undersigned, thereunto duly authorized in the City of
St. Louis and State of Missouri on the 28th day of September, 1998.

                                                SIGMA-ALDRICH CORPORATION
                                   
                                   
                                                By:  /S/Kirk A. Richter
                                   
                                                Kirk A. Richter, Treasurer
                                   
                             POWER OF ATTORNEY

     Each person whose signature appears below constitutes and
appoints Karen J. Miller, Thomas M. Tallarico and Kirk A. Richter,
and either of them, his or her true and lawful attorneys-in-fact
and agents, with full power of substitution and resubstitution, for
him or her and in his or her name, place and stead, in any and all
capacities, to sign any or all amendments to this registration
statement and to file the same, with all exhibits thereto and all
other documents in connection therewith with the Securities and
Exchange Commission, granting unto said attorneys-in-fact and
agents full power and authority to do and perform each and every
act and thing requisite and necessary to be done in and about the
premises, as fully as he or she might or could do in person, hereby
ratifying and confirming all that said attorneys-in-fact and agents
may lawfully do or cause to be done by virtue hereof.

     Pursuant to the requirements of the Securities Act of 1933,
this registration statement has been signed below by the following
persons on behalf of the Registrant and in the capacities and on
the dates indicated.

       Signature                     Title

/S/Carl T. Cori            Director, Chairman of the Board   September 28, 1998
   Carl T. Cori            and Chief Executive Officer                Date

/S/David R. Harvey        Director, President and            September 28, 1998
   David R. Harvey        Chief Operating Officer                     Date

/S/Karen J. Miller        Controller                         September 28, 1998
   Karen J. Miller                                                    Date

/S/Kirk A. Richter         Treasurer                         September 28, 1998
   Kirk A. Richter                                                    Date

/S/Thomas M. Tallarico     Vice President and Secretary      September 28, 1998
   Thomas M. Tallarico                                                Date

/S/David M. Kipnis         Director                          September 28, 1998
   David M. Kipnis                                                     Date

/S/Andrew E. Newman         Director                         September 28, 1998
   Andrew E. Newman                                                    Date

/S/Jerome W. Sandweiss      Director                         September 28, 1998
  Jerome W. Sandweiss                                                  Date

                                     EXHIBIT INDEX

Exhibit Number      Description
--------------      -----------
     
     4.1            Certificate of Incorporation, as
                    amended (incorporated by reference
                    to Exhibit 3(a) of Form 10-Q for
                    the quarter ended September 30,
                    1996, File No. 0-8135)
     
     4.2            By-Laws, as amended (incorporated
                    by reference to Exhibit 3(b) of
                    Form 10-K filed for year ended
                    December 31, 1997, File No. 0-8135)
     
     5.1            Opinion of Counsel
     
     10.1           Sigma-Aldrich Corporation
                    Directors' Nonqualified
                    Share Option Plan of 1998
                    (incorporated by reference to
                    Appendix A to the definitive Proxy
                    Statement dated March 27, 1998 for
                    the Company's Annual Meeting of
                    Shareholders held on May 5, 1998,
                    File No. 0-8135).
     
     23.1           Consent of Counsel (included in
                    Exhibit 5.1)
     
     23.2           Consent of Arthur Andersen LLP
     
     24.1           Power of Attorney (included on
                    signature page)