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                         TESTA, HURWITZ & THIBEAULT, LLP

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                                ATTORNEYS AT LAW

                                 125 High Street
                        Boston, Massachusetts 02110-2704
Office (617) 248-7000                                         Fax (617) 248-7100
Direct Dial:  (617) 248-7292                            E-Mail:  burnett@tht.com


                                January 26, 2005


VIA FAX AND EDGAR

United States Securities and Exchange Commission
450 Fifth Street, N.W.
Washington, D.C.  20549

Attention:  Mr. Russell Mancuso, Branch Chief
            Division of Corporation Finance

      Re:   Ionics, Incorporated
            Amendment No. 1 to Preliminary Schedule 14A submitted
              January 24, 2005
            File No. 001-07211

Dear Mr. Mancuso,

      On behalf of our client, Ionics, Incorporated (the "Company" or "Ionics"),
we are conveying the Company's responses to the comments of the Staff (the
"Staff") of the Division of Corporation Finance of the Securities and Exchange
Commission (the "Commission") contained in your letter dated January 25, 2005 to
Mr. Stephen Korn, the Company's Vice President and General Counsel (the "Comment
Letter"), with respect to the Company's response dated January 24, 2005 to the
Staff's Comment Letter dated January 21, 2005. Enclosed are pages from the
Amended Proxy Statement with the Company's proposed changes responsive to the
Staff's comments.

      The responses and supplementary information set forth below have been
organized in the same manner in which the Staff's comments were presented in the
Comment Letter. The information set forth in this letter is being provided on a
supplemental basis to the Staff. Copies of this letter and the attachments to it
are also being delivered under separate cover to Eduardo Aleman of the Staff.

OPINIONS OF IONICS' FINANCIAL ADVISORS - PAGE 21

COMMENT 1: WE HAVE CONSIDERED YOUR RESPONSE TO COMMENT 5 AND YOUR SUBSEQUENT
TELEPHONE CALLS. IF YOU BELIEVE THAT THE DOLLAR AMOUNT OF COMPENSATION NEED NOT
BE DISCLOSED IN THE PROXY STATEMENT, PLEASE INCLUDE NARRATIVE DISCLOSURE THAT
PROVIDES INVESTORS A CLEAR UNDERSTANDING OF THE MAGNITUDE OF THE AMOUNT PAID TO
THE FINANCIAL ADVISORS BY THE TARGET FOR THE FAIRNESS OPINIONS IN THIS
TRANSACTION RELATIVE TO THE AMOUNTS PAID BY THE ACQUIRER OVER THE PAST TWO
YEARS. INVESTORS SHOULD BE GIVEN AN OPPORTUNITY TO CONSIDER THIS INFORMATION,
ALONG WITH OTHER FACTORS THEY MAY CONSIDER


January 26, 2005
Page 2


MATERIAL, IN MAKING THEIR VOTING DECISIONS. ALSO DISCLOSE WHAT CONSIDERATION THE
IONICS BOARD GAVE THE ACQUIRER'S RELATIONSHIPS WITH THE FINANCIAL ADVISORS.

Company Response: Based on the conference call this morning with the Staff, the
Company proposes to make the changes to the disclosure reflected on pages 23 and
25 of the Amended Proxy Statement that are enclosed herewith and to add the
following paragraph as the second paragraph under the heading "Opinions of
Ionics' Financial Advisors":

            At the time of the engagements of Goldman Sachs and UBS, the Ionics
      board of directors was informed that Goldman Sachs and UBS had provided
      investment banking and other services to GE and had advised other
      companies in connection with transactions with GE. The Ionics board of
      directors received assurances from each of Goldman Sachs and UBS that it
      had not been engaged by GE with respect to a potential transaction with
      Ionics. The Ionics board of directors did not consider the amount of fees
      for investment banking and other services paid by GE to either Goldman
      Sachs or UBS.

COMMENT 2: PLEASE EXPAND YOUR DISCLOSURE IN RESPONSE TO COMMENT 3 TO CLARIFY HOW
USING TWO FIRMS WOULD ASSIST THE COMPANY IN OBTAINING THE HIGHEST VALUE FOR ITS
SHAREHOLDERS. YOU DISCLOSE THAT THE TERMS OF THE MERGER AGREEMENT, INCLUDING THE
CONSIDERATION TO BE PAID, WERE THE RESULT OF NEGOTIATIONS PRINCIPALLY BETWEEN
MESSRS. BROWN AND WOODBURN. IT APPEARS THAT THE CONSIDERATION HAD ALREADY BEEN
NEGOTIATED BETWEEN THE PARTIES, AND THAT EACH FINANCIAL ADVISOR WAS ENGAGED
MERELY TO RENDER AN OPINION AS TO THE FAIRNESS OF THE CONSIDERATION ALREADY
NEGOTIATED BETWEEN THE TWO PARTIES.

Company Response: The Company proposes to modify the disclosure in the first
paragraph under the heading "Opinions of Ionics' Financial Advisors" in the
Amended Proxy Statement in response to the Staff's comment, so that the entire
paragraph reads as follows:

            The Ionics board of directors selected both Goldman Sachs and UBS as
      its financial advisors because it believed that using the two firms would
      assist it in obtaining the highest value for Ionics stockholders. Both
      firms are internationally recognized investment banking firms that have
      substantial experience in transactions similar to the transaction
      contemplated by the Merger Agreement, have significant knowledge of and
      prior relationships with Ionics, and have significant knowledge of the
      industries in which Ionics conducts business. Both firms were engaged to
      act as Ionics' financial advisors at approximately the same time.
      Throughout the period of their engagements, both firms provided financial
      advice and assistance to Ionics in connection with the Merger, including
      assisting Ionics in analyzing the transaction; advising Ionics with
      respect to its negotiations with GE, Ionics' valuation and the terms and
      conditions of the transaction; and assisting in the diligence process, all
      of which Ionics believes helped it obtain the highest value for its
      stockholders. At the time of their engagements, the Ionics board of
      directors expected both firms to render their opinions as to the fairness,
      from a financial point of view, of the consideration to be paid in the
      Merger. At the meeting held on November 23, 2004, the Ionics board of
      directors requested that both firms provide their opinion as to the
      fairness, from a financial point of view, of the $44.00 in cash per share
      of Ionics common stock to be received by the holders of shares of Ionics
      common stock pursuant to the Merger Agreement. Obtaining opinions from
      both firms provided additional support for the determination by the Ionics
      board of directors as to the fairness


January 26, 2005
Page 3


      of the consideration to be received by Ionics' stockholders in the Merger.
      Ionics benefited from the combined expertise of the two firms, which
      collaborated in performing the financial analyses relating to their
      opinions, and the separate opinions rendered by their firms which
      demonstrated their independent conclusions, as further described herein,
      that the consideration to be received by Ionics' stockholders was fair as
      of the date of such opinions.

      While the terms of the Merger were negotiated principally between Messrs.
Brown and Woodburn, Goldman Sachs and UBS were engaged before the terms of the
Merger, including the structure of the transaction and the consideration to be
paid in the transaction, were negotiated and both were involved in advising and
assisting the Company in connection with the transaction. Disclosure to that
effect has been added in the paragraph that appears above. Goldman Sachs and UBS
were not, however, "engaged merely to render an opinion as to the fairness of
the consideration already negotiated between the two parties."

COMMENT 3: PLEASE MAKE YOUR DISCLOSURE REGARDING THE RELATIONSHIPS WITH THE
FINANCIAL ADVISORS MORE CLEAR. SEPARATE INTO DISTINCT PARAGRAPHS THE DISCLOSURE
REGARDING THE FEES PAID BY IONICS TO THE FINANCIAL ADVISORS. SIMILARLY, REVISE
TO DISCUSS THE WORK EACH FINANCIAL ADVISOR HAS PERFORMED FOR GE IN SEPARATE
PARAGRAPHS. AVOID EMBEDDED LISTS; INSTEAD USE BULLETS OR NUMBERED LISTS.

Company Response: The Company proposes to modify the disclosure in the Amended
Proxy Statement in response to the Staff's comment. See pages 23 and 25 of the
Amended Proxy Statement that are enclosed herewith.

FORM 8-K FILED DECEMBER 13, 2004

COMMENT 4: WE NOTE THAT ON NOVEMBER 23, 2004 - ONE DAY BEFORE THE PARTIES AGREED
TO THE MERGER, IONICS APPROVED CASH BONUS PAYMENTS TO 11 MANAGEMENT EMPLOYEES,
INCLUDING ITS NAMED EXECUTIVE OFFICERS, IN THE AMOUNT OF $870,000 WHICH ARE IN
ADDITION TO CONTRACTUALLY REQUIRED CASH BONUSES. WE NOTE THAT IT ALSO
ESTABLISHED TARGET BONUSES FOR MESSRS. BROWN, CURTIS, AND DICKERSON ON THAT
DATE. EXPAND TO DISCUSS THIS INFORMATION IN THE PROXY STATEMENT IF THESE ACTIONS
WERE RELATED TO THIS TRANSACTION IN ANY WAY. IF THEY WERE NOT RELATED TO THE GE
ACQUISITION, ADVISE SUPPLEMENTALLY IN A WRITTEN RESPONSE.

Company Response: The Company proposes to modify the disclosure in the Amended
Proxy Statement in response to the Staff's comment. See pages 7, 8, 32 and 33 of
the Amended Proxy Statement that are enclosed herewith.

COMMENT 5: PLEASE ALSO EXPLAIN WHY YOUR FORM 8-K WAS NOT TIMELY FILED.

Company Response: The Company mistakenly failed to timely file a Form 8-K with
respect to certain of the information contained in the above-referenced Form
8-K, but filed the above-referenced Form 8-K with that information promptly
after the mistake was discovered.

                                      * * *



January 26, 2005
Page 4


      If you have any questions with regard to these responses, need further
information or would like to discuss any of the matters covered in this letter,
please contact Mr. Korn at (617) 926-2500 or the undersigned at (617) 248-7292.

                                         Sincerely,


                                         /s/ Mark H. Burnett
                                         -------------------
                                         Mark H. Burnett

Enclosure

cc:      Eduardo Aleman
         Douglas R. Brown
         Stephen Korn, Esq.
         James W. Burns, Esq.
         Scott Seeley, Esq.
         Howard Chatzinoff, Esq.