As filed with the Securities and Exchange Commission on September 20, 1996
                             Registration No. 333-05345
                                                                     


                   SECURITIES AND EXCHANGE COMMISSION
                         Washington, D.C.  20549
                      ____________________________
                     POST-EFFECTIVE AMENDMENT NO. 1
                                   TO
                                FORM S-3
                         REGISTRATION STATEMENT
                                  UNDER
                       THE SECURITIES ACT OF 1933
                      ____________________________

                          IONICS, INCORPORATED
         (Exact name of registrant as specified in its charter)

   Massachusetts                                  04-2068530
(State or other jurisdic-                      (I.R.S. Employer
tion of incorporation                         Identification No.)
or organization)

                     _____________________________
                            65 Grove Street
                    Watertown, Massachusetts  02172
          (Address, including zip code, and telephone number,
   including area code of registrant's Principal Executive Offices)
                     _____________________________

                             Stephen Korn
                  Vice President and General Counsel
                         Ionics, Incorporated
                            65 Grove Street
                    Watertown, Massachusetts  02172
                            (617) 926-2500
            (Name, address and telephone number, including
                   area code, of agent for service)
                    ______________________________

   Approximate date of commencement of proposed sale to the public:
     Promptly after this registration statement becomes effective.
                    _______________________________


    


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    The Registrant hereby removes from registration under this
Registration Statement 76,442 shares of common stock, $1.00 par value
per share (the "Common Stock"), registered hereunder (all shares
originally registered hereunder being referred to as the "Offered
Shares") that have not been sold pursuant to this Registration
Statement.  By the terms of this Registration Statement and a
Registration Rights Agreement among the Registrant and certain holders
of Offered Shares, the Registrant was required to keep this
Registration Statement effective until September 12, 1996.  As of that
date, 61,357 Offered Shares had been sold or otherwise transferred by
selling stockholders under this Registration Statement.  Pursuant to
the Registrant's Undertaking in Item 17 of this Registration Statement,
the Registrant hereby removes from registration the 76,442 Offered
Shares that have not been sold pursuant to this Registration Statement
prior to the date hereof.































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                            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-3 and
has duly caused this Post-Effective Amendment No. 1 to Registration
Statement to be signed on its behalf by the undersigned, thereunto
duly authorized in the Town of Watertown and Commonwealth of
Massachusetts on the 20th day of September, 1996.

                           IONICS, INCORPORATED

                           By: /s/ Arthur L. Goldstein               
                           Arthur L. Goldstein, Chairman of the Board,
                           President and Chief Executive Officer     































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      Pursuant to the requirements of the Securities Act of 1933, this
Post-Effective Amendment No. 1 to the Registration Statement has been
signed by the following persons in the capacities and on the dates
indicated.

      Signature                       Title                 Date
                                                   
/s/Arthur L. Goldstein          Chairman of the Board,   September 20, 1996
Arthur L. Goldstein             President and Chief
                                Executive Officer
                                (Principal Executive Officer)

/s/Robert J. Halliday           Vice President,          September 20, 1996
Robert J. Halliday              Finance and 
                                and Chief Financial Officer
                                (Principal Financial
                                and Accounting Officer
/s/Douglas R. Brown*            Director              September 20, 1996
Douglas R. Brown

/s/William L. Brown*            Director              September 20, 1996
William L. Brown

/s/Arnaud de Vitry d'Avaucourt* Director              September 20, 1996
Arnaud de Vitry d'Avaucourt

/s/K. Kachadurian*              Director              September 20, 1996
K. Kachadurian

/s/Samuel A. Goldblith*         Director              September 20, 1996
Samuel A. Goldblith

/s/William E. Katz*             Director              September 20, 1996
William E. Katz

/s/Robert B. Luick*             Director              September 20, 1996
Robert B. Luick

/s/John J. Shields*             Director              September 20, 1996
John J. Shields

/s/Carl S. Sloane*              Director              September 20, 1996
Carl S. Sloane

/s/Mark S. Wrighton*            Director              September 20, 1996
Mark S. Wrighton

/s/Allen S. Wyett*              Director              September 20, 1996
Allen S. Wyett

*By:/s/Stephen Korn        
    Stephen Korn
    Attorney-in-fact
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