As filed with the Securities and Exchange Commission on June 20, 2000
                          Registration No. 333-
===============================================================================

                       SECURITIES AND EXCHANGE COMMISSION

                             WASHINGTON, D.C. 20549

                                    FORM S-8

                          REGISTRATION STATEMENT UNDER

                           THE SECURITIES ACT OF 1933

                              IONICS, INCORPORATED
              (Exact Name of Registrant as Specified in Its Charter)

       Delaware                                         04-2068530
(State or Other Jurisdiction of            (I.R.S. Employer Identification No.)
 Incorporation or Organization)

                                 65 Grove Street
                         Watertown, Massachusetts 02472
                    (Address of Principal Executive Offices)

                  ---------------------------------------------

            Ionics, Incorporated 1998 Non-Employee Directors' Fee Plan
                            (Full Title of the Plan)

                  ---------------------------------------------

                Stephen Korn, Vice President and General Counsel
                              Ionics, Incorporated
                                 65 Grove Street
                         Watertown, Massachusetts 02472
                     (Name and Address of Agent For Service)
                                 (617) 926-2500
          (Telephone Number, Including Area Code, of Agent For Service)

                  ---------------------------------------------

                                   Copies to:
                             William J. Schnoor, Jr.
                         Testa, Hurwitz & Thibeault, LLP
                                 125 High Street
                           Boston, Massachusetts 02110
                                 (617) 248-7000

===============================================================================
<TABLE>
<CAPTION>

                                                CALCULATION OF REGISTRATION FEE

                                                      Proposed Maximum          Proposed Maximum
 Title of Securities to        Amount to be            Offering Price               Aggregate               Amount of
      be Registered             Registered               Per Share               Offering Price         Registered Fee (1)
      -------------             ----------               ---------               --------------         ------------------
<S>                            <C>                        <C>                      <C>                       <C>
Common Stock, $1.00 par         4,338 shares             $29.03(2)                 $  125,932                $ 33.25
value                          95,662 shares              29.03(3)                 $2,777,068                $733.15

         Total:               100,000 shares              $29.03                   $2,903,000                $766.40
                              ==============

========================================================================================================================
</TABLE>

(1) Calculated pursuant to Section 6(b) of the Securities Act of 1933, as
amended.

(2) All of these  shares are  issued and  outstanding  and  available  for
resale hereunder.  Pursuant to Rule 457(h), the price of $29.03 per share, which
is the average of the high and low prices on the New York Stock Exchange on June
19, 2000, is set forth solely for purposes of calculating the filing fee.

(3) None of these shares have been issued.  Accordingly,  pursuant to Rule
457(h),  the price of $29.03 per share, which is the average of the high and low
prices on the New York Stock  Exchange on June 19, 2000, is set forth solely for
purposes of calculating the filing fee.

                                                                             -1-

<PAGE>

                                     PART I

A.       INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

Item 1.  Plan Information.

         The documents containing the information  specified in this Item 1 will
be sent or  given  to  employees,  directors  or  others  as  specified  by Rule
428(b)(1).  In accordance  with the rules and  regulations of the Securities and
Exchange  Commission (the  "Commission")  and the instructions to Form S-8, such
documents  are not  being  filed  with  the  Commission  either  as part of this
Registration  Statement or as prospectuses or prospectus supplements pursuant to
Rule 424.

Item 2.  Registrant Information and Employee Plan Annual Information.

         The documents containing the information  specified in this Item 2 will
be sent or given to employees as specified by Rule 428(b).  In  accordance  with
the rules and  regulations of the Commission and the  instructions  to Form S-8,
such  documents are not being filed with the  Commission  either as part of this
Registration  Statement or as prospectuses or prospectus supplements pursuant to
Rule 424.

B.       REOFFER PROSPECTUS STATEMENT

         The materials  that follow,  up to but not including the page beginning
Part II of this Registration Statement, constitute a Reoffer Prospectus prepared
in accordance  with the  requirements  of Part I of Form S-3 pursuant to General
Instruction  C  to  Form  S-8.  The  Reoffer  Prospectus  may  be  utilized  for
reofferings  and  resales  of up to 4,338  shares of common  stock  acquired  by
certain  affiliates  of Ionics,  Incorporated,  as defined in Rule 405 under the
Securities  Act of 1933,  as amended,  pursuant to Ionics,  Incorporated's  1998
Non-Employee Directors' Fee Plan.

                                                                             -2-


<PAGE>


                               REOFFER PROSPECTUS

                                  4,338 SHARES

                              Ionics, Incorporated

                                  Common Stock

                           (par value $1.00 per share)

                             -----------------------


         This reoffer  prospectus relates to 4,338 shares of the common stock of
Ionics,  Incorporated, a Massachusetts corporation ("Ionics"), which may be sold
from time to time by certain selling  stockholders of Ionics.  These shares were
issued  pursuant  to our 1998  Non-Employee  Directors'  Fee Plan.  The  selling
stockholders  may  sell  the  shares  from  time to  time,  subject  to  certain
restrictions. Ionics will receive no proceeds from the sale of these shares.

         Our  common  stock is traded on the New York Stock  Exchange  under the
symbol "ION." On June 19, 2000, the last reported sale price of our common stock
on the New York Stock Exchange was $28 7/8 per share.

                                ---------------



         NEITHER THE SECURITIES AND EXCHANGE COMMISSION NOR ANY STATE SECURITIES
REGULATORS  HAVE APPROVED OR  DISAPPROVED  OF THESE  SECURITIES OR DETERMINED IF
THIS PROSPECTUS IS TRUTHFUL OR COMPLETE. ANY REPRESENTATION TO THE CONTRARY IS A
CRIMINAL OFFENSE.

                                ---------------

               The date of this Reoffer  Prospectus  is June 20, 2000.

                                                                             -3-


<PAGE>


                              AVAILABLE INFORMATION

         This  prospectus  is part of a  registration  statement  on Form S-8 we
filed with the  Securities  and  Exchange  Commission  in  connection  with this
offering  and  does  not  contain  all  of  the  information   included  in  the
registration  statement.  Whenever a reference is made in this prospectus to any
contract or other document of ours,  the reference may not be complete,  and you
should refer to the exhibits that are a part of the registration statement for a
copy of the contract or document.

         In addition to the registration  statement,  we file annual,  quarterly
and current reports,  proxy statements and other information with the Securities
and Exchange  Commission.  You may read and copy the registration  statement and
any other documents we file at the Securities and Exchange  Commission's  Public
Reference Room at 450 Fifth Street, N.W., Washington, DC 20549. You may call the
Securities and Exchange  Commission at 1-800-SEC-0330 for further information on
the Public Reference Room.

         In addition,  the  Securities and Exchange  Commission  maintains a web
site   (http://www.sec.gov)   that  contains  reports,   proxy  and  information
statements and other information  regarding registrants that file electronically
with the Securities and Exchange Commission.

         We will  provide  without  charge to each  person  who is  delivered  a
prospectus,  upon written or oral request, a copy of any or all of the documents
incorporated by reference  herein (other than exhibits to those documents unless
those exhibits are specifically incorporated by reference into those documents).
Requests for copies should be directed to Ionics, Incorporated, 65 Grove Street,
Watertown, Massachusetts 02472 (telephone: (617) 926-2500).

                                     -2-
                                                                             -4-



<PAGE>


                                   THE COMPANY

         Ionics is a leading water purification company engaged worldwide in the
supply of water and of water treatment  equipment through the use of proprietary
separations  technologies and systems.  Our products and services are used by us
or our customers to desalt  brackish  water and  seawater,  to purify and supply
bottled  water,  to treat water in the home,  to  manufacture  and supply  water
treatment  chemicals and ultrapure water, to process food products,  recycle and
reclaim  process  water and  wastewater,  and to  measure  levels of  waterborne
contaminants  and  pollutants.   Our  customers  include  industrial  companies,
consumers, municipalities and other governmental entities, and utilities.

         Over fifty years ago,  the Company  pioneered  the  development  of the
ion-exchange  membrane and the  electrodialysis  process.  Since that time,  the
Company has  expanded  its  separations  technology  base to include a number of
membrane and  non-membrane-based  separations processes which the Company refers
to as The Ionics Toolbox(R). These separations processes include electrodialysis
reversal (EDR),  reverse  osmosis (RO),  ultrafiltration  (UF),  microfiltration
(MF),  electrodeionization (EDI), electrolysis, ion exchange, carbon adsorption,
and  thermal  processes  such as  evaporation  and  crystallization,  as well as
solvent  extraction and recovery  processes.  We believe that we are the world's
leading manufacturer of ion-exchange membranes and of membrane-based systems for
the desalination of water.

         We were incorporated in Massachusetts in 1948. Our principal  executive
offices are located at 65 Grove Street, Watertown, Massachusetts 02472.

         This   prospectus   contains   certain   "forward-looking   statements"
(statements  that are not  historical  fact) based on our current  expectations,
assumptions, estimates and projections about our Company and our industry. These
forward-looking  statements involve risks and uncertainties.  Our actual results
could  differ  materially  from  those  anticipated  in  those   forward-looking
statements as a result of many factors,  as more fully  described in our filings
with the Securities and Exchange Commission.

                                 USE OF PROCEEDS

         Ionics will not receive any proceeds from the sale of shares by the
 selling stockholders.  See "Selling Stockholders" and "Plan of Distribution."


                                     -3-
                                                                             -5-


<PAGE>


                              SELLING STOCKHOLDERS

         The following table sets forth the name of each selling stockholder and
(a) the number of shares of common stock each selling  stockholder  beneficially
owned as of the date of this  prospectus  and  prior to this  offering,  (b) the
number  of  shares  of  common  stock  being  offered  hereby  by  such  selling
stockholder  and (c) the number of shares of and the  percentage of common stock
outstanding to be beneficially owned by each selling stockholder  following this
offering,  assuming the sale of all shares by the selling  stockholders that are
registered  hereby.  There is no assurance that any of the selling  stockholders
will  participate  in this offering.  Each selling  stockholder is a director of
Ionics.

<TABLE>
<CAPTION>

                                                                                    Percentage of
                                                               Shares               Shares
                         Shares           Shares Covered       Beneficially         Beneficially
                         Beneficially     by this              Owned After          Owned After
    Name                 Owned (#)        Prospectus           this offering (#)    this Offering
    ----                 ---------        ----------           -----------------    -------------

<S>                      <C>                  <C>                <C>                     <C>
Douglas R. Brown         18,444 (1)           444                18,000 (1)              *

William L. Brown         18,782 (2)           782                18,000 (2)              *

Kathleen F. Feldstein     5,943 (3)           943                 4,500 (3)              *

John J. Shields          12,283 (4)           283                11,960 (4)              *

Daniel I.C. Wang          6,943 (5)           943                 6,000 (5)              *

Mark S. Wrighton         12,043 (6)           943                11,100 (6)              *
----------------
</TABLE>

#    The number of shares of common stock deemed  outstanding  as of the date of
     this  prospectus  for each  individual  includes  shares  of  common  stock
     outstanding on such date owned by such  individual and all shares of common
     stock subject to stock options held by such  individual  exercisable  as of
     the date of this prospectus or within 60 days thereafter.

*    Less than 1%

(1)  Includes 8,000 shares which Mr. Douglas R. Brown has the right to acquire
pursuant to the exercise of stock options.

(2)  Includes 15,000 shares which Mr. William L. Brown has the right to acquire
pursuant to the exercise of stock options.

(3)  Includes 4,000 shares which Ms. Feldstein has the right to acquire pursuant
to the exercise of stock options.

(4)  Includes 11,500 shares which Mr. Shields has the right to acquire pursuant
to the exercise of stock options.

(5)  Includes 6,000 shares which Mr. Wang has the right to acquire pursuant to
the exercise of stock options.

(6)  Includes 11,000 shares which Mr. Wrighton has the right to acquire pursuant
to the exercise of stock options.

                                    -4-
                                                                             -6-

<PAGE>


                              PLAN OF DISTRIBUTION

         The shares of our common stock offered  hereby may be sold from time to
time by the  selling  stockholders  for each of their own  account,  subject  to
certain  restrictions.  Ionics will receive no proceeds from this offering.  The
selling  stockholders will pay or assume brokerage  commissions or other charges
and expenses incurred in the sale of the shares.

         The selling stockholders' sale of their shares is not currently subject
to any underwriting agreement. The shares covered by this prospectus may be sold
by the selling stockholders or by pledgees, donees, transferees, distributees or
other successors in interest of the selling  stockholders from time to time. The
selling  stockholders  may sell their  shares from time to time at fixed  prices
that may be changed,  at market prices prevailing at the time of sale, at prices
related  to  prevailing  market  prices or at  negotiated  prices.  Sales may be
effected in the over-the-counter  market, on the New York Stock Exchange,  or on
any  exchange on which the shares may then be listed.  The selling  stockholders
may sell the  shares by one or more of the  following:  (a) in one or more block
trades  in which a broker or dealer so  engaged  will  attempt  to sell all or a
portion of the shares held by the selling stockholders as agent but may position
and resell a portion of the block as principal to  facilitate  the  transaction;
(b)  through  purchases  by a broker or dealer as  principal  and resale by such
broker or dealer for its account  pursuant to this  prospectus;  (c) in ordinary
brokerage transactions and transactions in which the broker solicits purchasers;
(d) in negotiated transactions; and (e) through other means.

         The  selling  stockholders  may effect  these  transactions  by selling
shares to or  through  broker-dealers,  and  those  broker-dealers  may  receive
compensation in the form of underwriting discounts, concessions, commissions, or
fees from the selling stockholders and/or purchasers of the shares for whom such
broker-dealers  may act as agent or to whom they may sell as principal,  or both
(which  compensation  to a  particular  broker-dealer  might  be  in  excess  of
customary commissions). These broker-dealers and the selling stockholders may be
deemed to be  "underwriters"  within  the  meaning  of the  Securities  Act,  in
connection with those sales, and any commissions received by them and any profit
on the  resale of  shares  placed  by them  might be  deemed to be  underwriting
compensation.

         Any shares of our common stock covered by this  Prospectus that qualify
for sale  pursuant to Rule 144 under the  Securities  Act may be sold under Rule
144 rather than pursuant to this  Prospectus.  The selling  stockholders are not
restricted as to the price or prices at which they may sell their shares.  Sales
of shares of common stock at less than the market  prices may depress the market
price of our common stock.  The selling  stockholders  are  restricted as to the
number of  shares  which may be sold at any one time  pursuant  to Rule 144.  In
addition, the selling stockholders may decide not to sell all, none or a portion
of their shares.

         We have informed the selling  stockholders  that the  anti-manipulation
rules under the  Exchange Act  (including,  without  limitation,  Rule 10b-5 and
Regulation  M - Rule 102) may apply to sales in the market  and we will  furnish
the selling  stockholders  upon request with a copy of these Rules. We will also
inform  the  selling  stockholders  of the need for  delivery  of copies of this
prospectus.

         State  Street Bank and Trust  Company,  Boston,  Massachusetts,  is the
transfer agent for our common stock.

                                    -5-
                                                                             -7-



<PAGE>


                                  LEGAL MATTERS

         Certain legal matters in connection  with the offering of the shares of
Common  Stock of the  Company  are being  passed upon for the Company by Stephen
Korn, Vice President,  General Counsel and Clerk of the Company. Mr. Korn is the
beneficial  owner of 90,086 shares of Common Stock,  including  88,000 presently
exercisable  stock options and 863 shares held in the Company's  Section  401(k)
Stock Savings Plan (based on January 31, 2000 plan data).

                INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

         The following documents filed by us with the Commission pursuant to the
Exchange Act are incorporated in this prospectus by reference:

1.   The  Registrant's  Annual  Report on Form 10-K for the  fiscal
     year ended  December 31, 1999 filed pursuant to the Securities
     Exchange  Act of 1934,  as  amended,  which  contains  audited
     financial  statements  for the fiscal year ended  December 31,
     1999.

2.   The Registrant's  Quarterly Report on Form 10-Q for the fiscal
     quarter ended March 31, 2000 filed  pursuant to the Securities
     Exchange Act of 1934,  as amended,  which  contains  unaudited
     financial  statements  for the fiscal  quarter ended March 31,
     2000.

3.   The description of the Company's Common Stock contained in the
     Company's  Registration  Statement on Form 8-A filed under the
     Securities  Exchange  Act of 1934,  as  amended,  pursuant  to
     Section 12 thereof.

         All documents  subsequently  filed by Ionics pursuant to Section 13(a),
13(c),  14 or 15(d)  of the  Exchange  Act,  prior  to the  termination  of this
offering,  shall be deemed incorporated by reference in this prospectus and made
a part  hereof  from  the  date of  filing  of those  documents.  Any  statement
contained in a document incorporated or deemed incorporated by reference in this
prospectus  shall  be  deemed  modified  or  superseded  for  purposes  of  this
prospectus  to the  extent  that a  statement  contained  herein or in any other
subsequently filed document which also is or is deemed incorporated by reference
herein or in any prospectus  supplement  modifies or supersedes  that statement.
Any  statement  so  modified  or  superseded  shall not be deemed,  except as so
modified or superseded, to constitute a part of this prospectus.

                                    -6-
                                                                             -8-


<PAGE>



===============================================================================

You should rely only on the information  contained in this  prospectus.  We have
not  authorized  anyone to  provide  you with  information  different  from that
contained in this prospectus. The selling stockholders are offering to sell, and
seeking offers to buy, shares of Common Stock only in jurisdictions where offers
and sales  are  permitted.  The  information  contained  in this  prospectus  is
accurate  only as of the  date of this  prospectus,  regardless  of the  time of
delivery  of  this  prospectus  or of any  sale  of the  Common  Stock.  In this
prospectus,  references  to  "Ionics,"  "we,"  "our" and "us"  refer to  Ionics,
Incorporated.

                                -----------------



                 TABLE OF CONTENTS

                                               Page

Available Information ......................     2
Ionics......................................     3
Use of Proceeds ............................     3
Selling Stockholders........................     4
Plan of Distribution .......................     5
Legal Matters ..............................     6
Incorporation of Certain Information
  by Reference..............................     6


===============================================================================


                                  4,338 Shares

                             Ionics, Incorporated

                                  4,338 Shares

                                  Common Stock

                                 ---------------

                                     REOFFER
                                    PROSPECTUS

                                 ---------------



                                  June 20, 2000

===============================================================================

                                       -9-


<PAGE>


                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3.  Incorporation of Documents by Reference.

         The following  documents filed with the Commission are  incorporated by
reference in this Registration Statement:

         (a) The  Registrant's  Annual  Report on Form 10-K for the fiscal  year
ended December 31, 1999 filed  pursuant to the Securities  Exchange Act of 1934,
as amended,  which  contains  audited  financial  statements for the fiscal year
ended December 31, 1999.

         (b) The  Registrant's  Quarterly  Report  on Form  10-Q for the  fiscal
quarter ended March 31, 2000 filed  pursuant to the  Securities  Exchange Act of
1934, as amended,  which contains unaudited financial  statements for the fiscal
quarter ended March 31, 2000.

         (c) All other  documents  filed by the  Registrant  pursuant to Section
13(a) or 15(d) of the Securities Exchange Act of 1934, as amended, since the end
of the fiscal year covered by the annual report referred to in (a) above.

         (d) The  description  of the  Company's  Common Stock  contained in the
Company's Registration Statement on Form 8-A filed under the Securities Exchange
Act of 1934, as amended, pursuant to Section 12 thereof.

         All documents  subsequently  filed by the Company  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
hereby have been sold or which deregisters all securities then remaining unsold,
shall be deemed to be incorporated  by reference  herein and to be a part hereof
from the date of filing of such documents.

         Any  statement  contained  in a document  incorporated  or deemed to be
incorporated  by reference  herein shall be deemed to be modified or  superseded
for  purposes  of this  Registration  Statement  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  part of this  Registration
Statement.

Item 4.  Description of Securities.

      Not applicable.

Item 5.  Interests of Named Experts and Counsel.

      Certain  legal  matters in  connection  with the offering of the shares of
Common  Stock of the  Company  are being  passed upon for the Company by Stephen
Korn, Vice President,  General Counsel and Clerk of the Company. Mr. Korn is the
beneficial  owner of 90,086 shares of Common Stock,  including  88,000 presently
exercisable  stock options and 863 shares held in the Company's  Section  401(k)
Stock Savings Plan (based on January 31, 2000 plan data).

                                                                            -10-

<PAGE>

Item 6.  Indemnification of Directors and Officers.

      The Company is permitted by Massachusetts  law and required by its By-laws
to indemnify any director or officer or former  director or officer  against all
expenses and liabilities  reasonably  incurred by such person in connection with
any  legal  action in which  such  person  is  involved  by reason of his or her
position with the Company  unless he or she shall have been finally  adjudicated
in any  action,  suit or  proceeding  not to have  acted  in good  faith  in the
reasonable  belief  that  his or her  action  was in the best  interests  of the
Company.  Such indemnification  shall include payment by the Company of expenses
incurred in defending a civil or criminal action or proceeding in advance of the
final  disposition  of such action,  or defending a civil or criminal  action or
proceeding,  upon  the  Company's  receipt  of the  undertaking  of  the  person
indemnified  to repay  such  payment if such  person  shall be  adjudicated  not
entitled to such indemnification.

      Directors  and  officers  are also  insured up to an  aggregate  amount of
$10,000,000 under Directors' and Officers'  liability and Company  Reimbursement
Policies.

      The  Company's  Restated  Articles  of  Organization  include a  provision
limiting the personal liability of a director of the Company to its stockholders
for  monetary  damages  for  breaches  of  their  fiduciary  duty to the  extent
permitted by the Massachusetts Business Corporation Law.

      See Item 9(c) for a statement  concerning  indemnification for liabilities
under the Securities Act of 1933.

Item 7.  Exemption for Registration Claimed.

      Not applicable.

Item 8.  Exhibits.

Exhibit No.        Description of Exhibit
-----------        ----------------------

4.1                Renewed Rights Agreement, dated as of August 19, 1997 between
                   Ionics, Incorporated and BankBoston N.A. (filed as Exhibit 1
                   to the Company's Current Report on Form 8-K dated August 27,
                   1997).

4.2                Form of Common Stock Certificate (filed as Exhibit 4.2 to the
                   Company's Annual Report on Form 10-K for the year ended
                   December 31, 1995).

4.3                Ionics,  Incorporated 1998 Non-Employee Directors' Fee Plan
                   (filed as Exhibit 10.1 to the Company's Quarterly Report on
                   Form 10-Q for the quarterly period ended September 30, 1998).

5                  Opinion of Stephen Korn, General Counsel.

23.1               Consent of Stephen Korn, General Counsel (included in Exhibit
                   5 hereto).

23.2               Consent of PricewaterhouseCoopers LLP.

24                 Power of Attorney.

                                                                            -11-
<PAGE>

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 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;

                  (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.

                  (4) If the registrant is a foreign private issuer, to file a
                  post-effective amendment to the registration statement to
                  include any financial statements required by Rule 3-19 of this
                  chapter at the start of any delayed offering or throughout a
                  continuous offering.  Financial statements and information
                  otherwise required by Section 10(a)(3) of the Act need not
                  be furnished, provided, that the registrant includes in the
                  prospectus, by means of a post-effective amendment, financial
                  statements required pursuant to this paragraph (a)(4) and
                  other information necessary to ensure that all other
                  information in the prospectus is at least as current as the
                  date of those financial statements.  Notwithstanding the
                  foregoing, with respect to registration statements on Form
                  F-3, a post-effective amendment need not be filed to include
                  financial statements and information required by Section
                  10(a)(3) of the Act or Rule 3-19 of this chapter if such
                  financial statements and information are 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 Form F-3.

                                                                            -12-
<PAGE>

(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 Section 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.


                                                                            -13-

<PAGE>

                                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 Town of Watertown, in the Commonwealth of Massachusetts,  on
this 20th day of June, 2000.

                                        IONICS, INCORPORATED

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


         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.

                                         /s/ Arthur L. Goldstein
                                         -----------------------
Date:  June 20, 2000                     Arthur L. Goldstein,
                                         Chairman of the Board, President and
                                         Chief Executive Officer (principal
                                         executive officer) and Director


                                         /s/ Robert J. Halliday
                                         ----------------------
Date: June 20, 2000                      Robert J. Halliday,
                                         Executive Vice President, Chief
                                         Operating Officer and Chief
                                         Financial Officer (principal financial
                                         officer)


                                                                            -14-


<PAGE>


Pursuant to the  requirements of the Securities Act of 1933,  this  Registration
Statement has been signed by the following  persons in the capacities and on the
dates indicated.

             SIGNATURE                 TITLE                       DATE

/s/ Douglas R. Brown                                           June 20, 2000
--------------------
Douglas R. Brown                      Director


--------------------
Stephen L. Brown                      Director

/s/ William L. Brown                                           June 20, 2000
--------------------
William L. Brown                      Director

/s/ Arnaud de Vitry d'Avaucourt                                June 20, 2000
-------------------------------
Arnaud de Vitry d'Avaucourt           Director

/s/ Kathleen F. Feldstein                                      June 20, 2000
-------------------------
Kathleen F. Feldstein                 Director

/s/ Arthur L. Goldstein               Chairman of the Board    June 20, 2000
-----------------------               and Director
Arthur L. Goldstein

/s/ William E. Katz                   Director                 June 20, 2000
-------------------
William E. Katz

                                      Director
------------------
William K. Reilly

/s/ John J. Shields                   Director                  June 20, 2000
-------------------
John J. Shields

/s/ Carl S. Sloane                    Director                  June 20, 2000
------------------
Carl S. Sloane

/s/ Daniel I. C. Wang                 Director                  June 20, 2000
---------------------
Daniel I. C. Wang

/s/ Mark S. Wrighton                  Director                  June 20, 2000
--------------------
Mark S. Wrighton

/s/ Allen S. Wyett                    Director                  June 20, 2000
------------------
Allen S. Wyett

                                                                            -15-


<PAGE>



                                  EXHIBIT INDEX

Exhibit No.        Description of Exhibit
-----------        ----------------------

4.1                Renewed Rights Agreement, dated as of August 19, 1997 between
                   Ionics, Incorporated and BankBoston N.A. (filed as Exhibit 1
                   to the Company's Current Report on Form 8-K dated August 27,
                   1997).

4.2                Form of Common Stock Certificate (filed as Exhibit 4.2 to the
                   Company's Annual Report on Form 10-K for the year ended
                   December 31, 1995).

4.3                Ionics,  Incorporated 1998 Non-Employee Directors' Fee
                   Plan (filed as Exhibit 10.1 to the Company's Quarterly
                   Report on Form  10-Q for the  quarterly  period  ended
                   September 30, 1998).

5                  Opinion of Stephen Korn, General Counsel            (p. 17)

23.1               Consent of Stephen Korn, General Counsel (included in Exhibit
                   5 hereto)                                           (p. 17)

23.2               Consent of PricewaterhouseCoopers LLP               (p. 18)

24                 Power of Attorney                                   (p. 19)


                                                                            -16-


<PAGE>
                                   EXHIBIT 5

                              Ionics, Incorporated

                                 65 Grove Street

                         Watertown, Massachusetts 02472

                                                              June 20, 2000
Ionics, Incorporated
65 Grove Street
Watertown, MA 02172

         Re:      Registration Statement on Form S-8 relating to the Ionics,
                  Incorporated 1998 Non-Employee Directors' Fee Plan
Gentlemen:

         As  General   Counsel  for  Ionics,   Incorporated,   a   Massachusetts
corporation  (the  "Company"),  I am familiar  with its  corporate  affairs.  In
particular,  I have acted as counsel  for the  Company  in  connection  with the
registration  of 100,000 shares of the Company's  common stock,  par value $1.00
per share (the "Shares"),  reserved for issuance under the Ionics,  Incorporated
1998 Non-Employee  Directors' Fee Plan (the "Plan"),  pursuant to a Registration
Statement on Form S-8 (the "Registration Statement") under the Securities Act of
1933,  as amended,  and the conduct of certain  corporate  proceedings  relating
thereto.

         As such counsel,  I have examined and am familiar with the Registration
Statement,  certain  corporate  records of the Company,  including  its Restated
Articles of Organization,  as amended,  its By-laws,  minutes of meetings of its
Board of Directors and stockholders,  and such other documents,  instruments and
certificates of government  officials as I have deemed  necessary as a basis for
the opinions herein expressed.

         In my examination described in the preceding paragraph,  I have assumed
the genuineness of all signatures,  the authenticity of all documents  submitted
to me as  originals,  the  conformity  to  the  corresponding  originals  of all
documents  submitted to me as copies,  the authenticity of the originals of such
copies, and the accuracy and completeness of all corporate records.

         I have made such  examination  of  Massachusetts  law as I have  deemed
relevant for purposes of this opinion,  but have not made any review of the laws
of any other  state or  jurisdiction.  Accordingly,  this  opinion is limited to
Massachusetts law.

         Based upon and subject to the  foregoing,  I am of the opinion that the
Shares to be issued by the Company  from time to time  pursuant to the Plan will
be duly authorized, validly issued, fully paid and non-assessable.

         I hereby  consent  to the  filing of this  opinion as an exhibit to the
Registration  Statement and to the reference to me in Item 5, Interests of Named
Experts  and  Counsel,  in the  Registration  Statement.  This  opinion is being
furnished to you solely for the foregoing use and, other than in connection with
such use, is not to be  disseminated,  reproduced or published in any form, used
for any other  purpose or relied upon by any other  person or entity  without my
prior written consent.

Very truly yours,


/s/Stephen Korn
---------------
Stephen Korn
General Counsel

                                                                            -17-


<PAGE>



                                                                   EXHIBIT 23.2

                       CONSENT OF INDEPENDENT ACCOUNTANTS

         We  hereby   consent  to  the   incorporation   by  reference  in  this
Registration  Statement  on Form S-8 of our report,  dated  February  22,  2000,
relating to the financial statements and financial statement schedule of Ionics,
Incorporated,  which appears in Ionics,  Incorporated Annual Report on Form 10-K
for the year ended December 31, 1999.

PricewaterhouseCoopers LLP
Boston, MA
June 19, 2000


                                                                            -18-


<PAGE>

                                                                     EXHIBIT 24

                                POWER OF ATTORNEY

         We, the  undersigned  Officers and  Directors of Ionics,  Incorporated,
hereby  severally  constitute  Arthur L.  Goldstein and Stephen Korn and each of
them to sign  for and in their  names in the  capacities  indicated  below,  the
Registration  Statement on Form S-8 dated June 20, 2000, herewith filed with the
Securities and Exchange  Commission,  and any and all amendments thereto for the
purpose of  registering  shares of Common Stock,  par value $1.00 per share,  of
Ionics, Incorporated, hereby ratifying and confirming our signatures as they may
be  signed  by our  attorneys  to such  Registration  Statement  and any and all
amendments to such Registration Statement.

         Witness our hands on the respective dates set forth below.
<TABLE>
<CAPTION>

             SIGNATURE                             TITLE                                DATE
             ---------                             -----                                ----
<S>                           <C>                                                   <C>
/s/ Arthur L. Goldstein       Chairman of the  Board,  Chief Executive Officer
-----------------------       and President (principal executive officer) and
Arthur L. Goldstein           Director                                              June 20, 2000

/s/ Douglas R. Brown

--------------------
Douglas R. Brown                      Director                                      June 20, 2000


----------------
Stephen L. Brown                      Director

/s/ William L. Brown
--------------------
William L. Brown                      Director                                      June 20, 2000

/s/ Arnaud de Vitry d'Avaucourt
-------------------------------
Arnaud de Vitry d'Avaucourt           Director                                      June 20, 2000

/s/ Kathleen F. Feldstein
-------------------------
Kathleen F. Feldstein                 Director                                      June 20, 2000

/s/ William E. Katz
-------------------
William E. Katz                       Director                                      June 20, 2000


-----------------
William K. Reilly                     Director

/s/ John J. Shields
-------------------
John J. Shields                       Director                                      June 20, 2000

/s/ Carl S. Sloane
------------------
Carl S. Sloane                        Director                                      June 20, 2000

/s/ Daniel I. C. Wang
---------------------
Daniel I.C. Wang                      Director                                      June 20, 2000

/s/ Mark S. Wrighton
--------------------
Mark S. Wrighton                      Director                                      June 20, 2000

/s/ Allen S. Wyett
------------------
Allen S. Wyett                        Director                                      June 20, 2000




                                                                            -19-
</TABLE>
[{"type": "S-8", "sequence": "1", "filename": "0001.txt", "description": "REGISTRATION STATEMENT", "secsgml_size_bytes": 48368}]
{"company-data": {"conformed-name": "IONICS INC", "cik": "0000052466", "assigned-sic": "3559", "irs-number": "042068530", "state-of-incorporation": "MA", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-39684", "film-number": "657566"}, "business-address": {"street1": "65 GROVE ST", "city": "WATERTOWN", "state": "MA", "zip": "02172", "phone": "6179262500"}}
As filed with the Securities and Exchange Commission on June 20, 2000
                          Registration No. 333-
===============================================================================

                       SECURITIES AND EXCHANGE COMMISSION

                             WASHINGTON, D.C. 20549

                                    FORM S-8

                          REGISTRATION STATEMENT UNDER

                           THE SECURITIES ACT OF 1933

                              IONICS, INCORPORATED
              (Exact Name of Registrant as Specified in Its Charter)

       Delaware                                         04-2068530
(State or Other Jurisdiction of            (I.R.S. Employer Identification No.)
 Incorporation or Organization)

                                 65 Grove Street
                         Watertown, Massachusetts 02472
                    (Address of Principal Executive Offices)

                  ---------------------------------------------

            Ionics, Incorporated 1998 Non-Employee Directors' Fee Plan
                            (Full Title of the Plan)

                  ---------------------------------------------

                Stephen Korn, Vice President and General Counsel
                              Ionics, Incorporated
                                 65 Grove Street
                         Watertown, Massachusetts 02472
                     (Name and Address of Agent For Service)
                                 (617) 926-2500
          (Telephone Number, Including Area Code, of Agent For Service)

                  ---------------------------------------------

                                   Copies to:
                             William J. Schnoor, Jr.
                         Testa, Hurwitz & Thibeault, LLP
                                 125 High Street
                           Boston, Massachusetts 02110
                                 (617) 248-7000

===============================================================================
CALCULATION OF REGISTRATION FEE

                                                      Proposed Maximum          Proposed Maximum
 Title of Securities to        Amount to be            Offering Price               Aggregate               Amount of
      be Registered             Registered               Per Share               Offering Price         Registered Fee (1)
      -------------             ----------               ---------               --------------         ------------------
Common Stock, $1.00 par         4,338 shares             $29.03(2)                 $  125,932                $ 33.25
value                          95,662 shares              29.03(3)                 $2,777,068                $733.15

         Total:               100,000 shares              $29.03                   $2,903,000                $766.40
                              ==============

========================================================================================================================
(1) Calculated pursuant to Section 6(b) of the Securities Act of 1933, as
amended.

(2) All of these  shares are  issued and  outstanding  and  available  for
resale hereunder.  Pursuant to Rule 457(h), the price of $29.03 per share, which
is the average of the high and low prices on the New York Stock Exchange on June
19, 2000, is set forth solely for purposes of calculating the filing fee.

(3) None of these shares have been issued.  Accordingly,  pursuant to Rule
457(h),  the price of $29.03 per share, which is the average of the high and low
prices on the New York Stock  Exchange on June 19, 2000, is set forth solely for
purposes of calculating the filing fee.

                                                                             -1-
PART I

A.       INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

Item 1.  Plan Information.

         The documents containing the information  specified in this Item 1 will
be sent or  given  to  employees,  directors  or  others  as  specified  by Rule
428(b)(1).  In accordance  with the rules and  regulations of the Securities and
Exchange  Commission (the  "Commission")  and the instructions to Form S-8, such
documents  are not  being  filed  with  the  Commission  either  as part of this
Registration  Statement or as prospectuses or prospectus supplements pursuant to
Rule 424.

Item 2.  Registrant Information and Employee Plan Annual Information.

         The documents containing the information  specified in this Item 2 will
be sent or given to employees as specified by Rule 428(b).  In  accordance  with
the rules and  regulations of the Commission and the  instructions  to Form S-8,
such  documents are not being filed with the  Commission  either as part of this
Registration  Statement or as prospectuses or prospectus supplements pursuant to
Rule 424.

B.       REOFFER PROSPECTUS STATEMENT

         The materials  that follow,  up to but not including the page beginning
Part II of this Registration Statement, constitute a Reoffer Prospectus prepared
in accordance  with the  requirements  of Part I of Form S-3 pursuant to General
Instruction  C  to  Form  S-8.  The  Reoffer  Prospectus  may  be  utilized  for
reofferings  and  resales  of up to 4,338  shares of common  stock  acquired  by
certain  affiliates  of Ionics,  Incorporated,  as defined in Rule 405 under the
Securities  Act of 1933,  as amended,  pursuant to Ionics,  Incorporated's  1998
Non-Employee Directors' Fee Plan.

                                                                             -2-
REOFFER PROSPECTUS

                                  4,338 SHARES

                              Ionics, Incorporated

                                  Common Stock

                           (par value $1.00 per share)

                             -----------------------

         This reoffer  prospectus relates to 4,338 shares of the common stock of
Ionics,  Incorporated, a Massachusetts corporation ("Ionics"), which may be sold
from time to time by certain selling  stockholders of Ionics.  These shares were
issued  pursuant  to our 1998  Non-Employee  Directors'  Fee Plan.  The  selling
stockholders  may  sell  the  shares  from  time to  time,  subject  to  certain
restrictions. Ionics will receive no proceeds from the sale of these shares.

         Our  common  stock is traded on the New York Stock  Exchange  under the
symbol "ION." On June 19, 2000, the last reported sale price of our common stock
on the New York Stock Exchange was $28 7/8 per share.

                                ---------------

         NEITHER THE SECURITIES AND EXCHANGE COMMISSION NOR ANY STATE SECURITIES
REGULATORS  HAVE APPROVED OR  DISAPPROVED  OF THESE  SECURITIES OR DETERMINED IF
THIS PROSPECTUS IS TRUTHFUL OR COMPLETE. ANY REPRESENTATION TO THE CONTRARY IS A
CRIMINAL OFFENSE.

                                ---------------

               The date of this Reoffer  Prospectus  is June 20, 2000.

                                                                             -3-
AVAILABLE INFORMATION

         This  prospectus  is part of a  registration  statement  on Form S-8 we
filed with the  Securities  and  Exchange  Commission  in  connection  with this
offering  and  does  not  contain  all  of  the  information   included  in  the
registration  statement.  Whenever a reference is made in this prospectus to any
contract or other document of ours,  the reference may not be complete,  and you
should refer to the exhibits that are a part of the registration statement for a
copy of the contract or document.

         In addition to the registration  statement,  we file annual,  quarterly
and current reports,  proxy statements and other information with the Securities
and Exchange  Commission.  You may read and copy the registration  statement and
any other documents we file at the Securities and Exchange  Commission's  Public
Reference Room at 450 Fifth Street, N.W., Washington, DC 20549. You may call the
Securities and Exchange  Commission at 1-800-SEC-0330 for further information on
the Public Reference Room.

         In addition,  the  Securities and Exchange  Commission  maintains a web
site   (http://www.sec.gov)   that  contains  reports,   proxy  and  information
statements and other information  regarding registrants that file electronically
with the Securities and Exchange Commission.

         We will  provide  without  charge to each  person  who is  delivered  a
prospectus,  upon written or oral request, a copy of any or all of the documents
incorporated by reference  herein (other than exhibits to those documents unless
those exhibits are specifically incorporated by reference into those documents).
Requests for copies should be directed to Ionics, Incorporated, 65 Grove Street,
Watertown, Massachusetts 02472 (telephone: (617) 926-2500).

                                     -2-
                                                                             -4-
THE COMPANY

         Ionics is a leading water purification company engaged worldwide in the
supply of water and of water treatment  equipment through the use of proprietary
separations  technologies and systems.  Our products and services are used by us
or our customers to desalt  brackish  water and  seawater,  to purify and supply
bottled  water,  to treat water in the home,  to  manufacture  and supply  water
treatment  chemicals and ultrapure water, to process food products,  recycle and
reclaim  process  water and  wastewater,  and to  measure  levels of  waterborne
contaminants  and  pollutants.   Our  customers  include  industrial  companies,
consumers, municipalities and other governmental entities, and utilities.

         Over fifty years ago,  the Company  pioneered  the  development  of the
ion-exchange  membrane and the  electrodialysis  process.  Since that time,  the
Company has  expanded  its  separations  technology  base to include a number of
membrane and  non-membrane-based  separations processes which the Company refers
to as The Ionics Toolbox(R). These separations processes include electrodialysis
reversal (EDR),  reverse  osmosis (RO),  ultrafiltration  (UF),  microfiltration
(MF),  electrodeionization (EDI), electrolysis, ion exchange, carbon adsorption,
and  thermal  processes  such as  evaporation  and  crystallization,  as well as
solvent  extraction and recovery  processes.  We believe that we are the world's
leading manufacturer of ion-exchange membranes and of membrane-based systems for
the desalination of water.

         We were incorporated in Massachusetts in 1948. Our principal  executive
offices are located at 65 Grove Street, Watertown, Massachusetts 02472.

         This   prospectus   contains   certain   "forward-looking   statements"
(statements  that are not  historical  fact) based on our current  expectations,
assumptions, estimates and projections about our Company and our industry. These
forward-looking  statements involve risks and uncertainties.  Our actual results
could  differ  materially  from  those  anticipated  in  those   forward-looking
statements as a result of many factors,  as more fully  described in our filings
with the Securities and Exchange Commission.

                                 USE OF PROCEEDS

         Ionics will not receive any proceeds from the sale of shares by the
 selling stockholders.  See "Selling Stockholders" and "Plan of Distribution."

                                     -3-
                                                                             -5-
SELLING STOCKHOLDERS

         The following table sets forth the name of each selling stockholder and
(a) the number of shares of common stock each selling  stockholder  beneficially
owned as of the date of this  prospectus  and  prior to this  offering,  (b) the
number  of  shares  of  common  stock  being  offered  hereby  by  such  selling
stockholder  and (c) the number of shares of and the  percentage of common stock
outstanding to be beneficially owned by each selling stockholder  following this
offering,  assuming the sale of all shares by the selling  stockholders that are
registered  hereby.  There is no assurance that any of the selling  stockholders
will  participate  in this offering.  Each selling  stockholder is a director of
Ionics.
Percentage of
                                                               Shares               Shares
                         Shares           Shares Covered       Beneficially         Beneficially
                         Beneficially     by this              Owned After          Owned After
    Name                 Owned (#)        Prospectus           this offering (#)    this Offering
    ----                 ---------        ----------           -----------------    -------------
Douglas R. Brown         18,444 (1)           444                18,000 (1)              *

William L. Brown         18,782 (2)           782                18,000 (2)              *

Kathleen F. Feldstein     5,943 (3)           943                 4,500 (3)              *

John J. Shields          12,283 (4)           283                11,960 (4)              *

Daniel I.C. Wang          6,943 (5)           943                 6,000 (5)              *

Mark S. Wrighton         12,043 (6)           943                11,100 (6)              *
----------------
#    The number of shares of common stock deemed  outstanding  as of the date of
     this  prospectus  for each  individual  includes  shares  of  common  stock
     outstanding on such date owned by such  individual and all shares of common
     stock subject to stock options held by such  individual  exercisable  as of
     the date of this prospectus or within 60 days thereafter.

*    Less than 1%

(1)  Includes 8,000 shares which Mr. Douglas R. Brown has the right to acquire
pursuant to the exercise of stock options.

(2)  Includes 15,000 shares which Mr. William L. Brown has the right to acquire
pursuant to the exercise of stock options.

(3)  Includes 4,000 shares which Ms. Feldstein has the right to acquire pursuant
to the exercise of stock options.

(4)  Includes 11,500 shares which Mr. Shields has the right to acquire pursuant
to the exercise of stock options.

(5)  Includes 6,000 shares which Mr. Wang has the right to acquire pursuant to
the exercise of stock options.

(6)  Includes 11,000 shares which Mr. Wrighton has the right to acquire pursuant
to the exercise of stock options.

                                    -4-
                                                                             -6-
PLAN OF DISTRIBUTION

         The shares of our common stock offered  hereby may be sold from time to
time by the  selling  stockholders  for each of their own  account,  subject  to
certain  restrictions.  Ionics will receive no proceeds from this offering.  The
selling  stockholders will pay or assume brokerage  commissions or other charges
and expenses incurred in the sale of the shares.

         The selling stockholders' sale of their shares is not currently subject
to any underwriting agreement. The shares covered by this prospectus may be sold
by the selling stockholders or by pledgees, donees, transferees, distributees or
other successors in interest of the selling  stockholders from time to time. The
selling  stockholders  may sell their  shares from time to time at fixed  prices
that may be changed,  at market prices prevailing at the time of sale, at prices
related  to  prevailing  market  prices or at  negotiated  prices.  Sales may be
effected in the over-the-counter  market, on the New York Stock Exchange,  or on
any  exchange on which the shares may then be listed.  The selling  stockholders
may sell the  shares by one or more of the  following:  (a) in one or more block
trades  in which a broker or dealer so  engaged  will  attempt  to sell all or a
portion of the shares held by the selling stockholders as agent but may position
and resell a portion of the block as principal to  facilitate  the  transaction;
(b)  through  purchases  by a broker or dealer as  principal  and resale by such
broker or dealer for its account  pursuant to this  prospectus;  (c) in ordinary
brokerage transactions and transactions in which the broker solicits purchasers;
(d) in negotiated transactions; and (e) through other means.

         The  selling  stockholders  may effect  these  transactions  by selling
shares to or  through  broker-dealers,  and  those  broker-dealers  may  receive
compensation in the form of underwriting discounts, concessions, commissions, or
fees from the selling stockholders and/or purchasers of the shares for whom such
broker-dealers  may act as agent or to whom they may sell as principal,  or both
(which  compensation  to a  particular  broker-dealer  might  be  in  excess  of
customary commissions). These broker-dealers and the selling stockholders may be
deemed to be  "underwriters"  within  the  meaning  of the  Securities  Act,  in
connection with those sales, and any commissions received by them and any profit
on the  resale of  shares  placed  by them  might be  deemed to be  underwriting
compensation.

         Any shares of our common stock covered by this  Prospectus that qualify
for sale  pursuant to Rule 144 under the  Securities  Act may be sold under Rule
144 rather than pursuant to this  Prospectus.  The selling  stockholders are not
restricted as to the price or prices at which they may sell their shares.  Sales
of shares of common stock at less than the market  prices may depress the market
price of our common stock.  The selling  stockholders  are  restricted as to the
number of  shares  which may be sold at any one time  pursuant  to Rule 144.  In
addition, the selling stockholders may decide not to sell all, none or a portion
of their shares.

         We have informed the selling  stockholders  that the  anti-manipulation
rules under the  Exchange Act  (including,  without  limitation,  Rule 10b-5 and
Regulation  M - Rule 102) may apply to sales in the market  and we will  furnish
the selling  stockholders  upon request with a copy of these Rules. We will also
inform  the  selling  stockholders  of the need for  delivery  of copies of this
prospectus.

         State  Street Bank and Trust  Company,  Boston,  Massachusetts,  is the
transfer agent for our common stock.

                                    -5-
                                                                             -7-
LEGAL MATTERS

         Certain legal matters in connection  with the offering of the shares of
Common  Stock of the  Company  are being  passed upon for the Company by Stephen
Korn, Vice President,  General Counsel and Clerk of the Company. Mr. Korn is the
beneficial  owner of 90,086 shares of Common Stock,  including  88,000 presently
exercisable  stock options and 863 shares held in the Company's  Section  401(k)
Stock Savings Plan (based on January 31, 2000 plan data).

                INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

         The following documents filed by us with the Commission pursuant to the
Exchange Act are incorporated in this prospectus by reference:

1.   The  Registrant's  Annual  Report on Form 10-K for the  fiscal
     year ended  December 31, 1999 filed pursuant to the Securities
     Exchange  Act of 1934,  as  amended,  which  contains  audited
     financial  statements  for the fiscal year ended  December 31,
     1999.

2.   The Registrant's  Quarterly Report on Form 10-Q for the fiscal
     quarter ended March 31, 2000 filed  pursuant to the Securities
     Exchange Act of 1934,  as amended,  which  contains  unaudited
     financial  statements  for the fiscal  quarter ended March 31,
     2000.

3.   The description of the Company's Common Stock contained in the
     Company's  Registration  Statement on Form 8-A filed under the
     Securities  Exchange  Act of 1934,  as  amended,  pursuant  to
     Section 12 thereof.

         All documents  subsequently  filed by Ionics pursuant to Section 13(a),
13(c),  14 or 15(d)  of the  Exchange  Act,  prior  to the  termination  of this
offering,  shall be deemed incorporated by reference in this prospectus and made
a part  hereof  from  the  date of  filing  of those  documents.  Any  statement
contained in a document incorporated or deemed incorporated by reference in this
prospectus  shall  be  deemed  modified  or  superseded  for  purposes  of  this
prospectus  to the  extent  that a  statement  contained  herein or in any other
subsequently filed document which also is or is deemed incorporated by reference
herein or in any prospectus  supplement  modifies or supersedes  that statement.
Any  statement  so  modified  or  superseded  shall not be deemed,  except as so
modified or superseded, to constitute a part of this prospectus.

                                    -6-
                                                                             -8-
===============================================================================

You should rely only on the information  contained in this  prospectus.  We have
not  authorized  anyone to  provide  you with  information  different  from that
contained in this prospectus. The selling stockholders are offering to sell, and
seeking offers to buy, shares of Common Stock only in jurisdictions where offers
and sales  are  permitted.  The  information  contained  in this  prospectus  is
accurate  only as of the  date of this  prospectus,  regardless  of the  time of
delivery  of  this  prospectus  or of any  sale  of the  Common  Stock.  In this
prospectus,  references  to  "Ionics,"  "we,"  "our" and "us"  refer to  Ionics,
Incorporated.

                                -----------------

                 TABLE OF CONTENTS

                                               Page

Available Information ......................     2
Ionics......................................     3
Use of Proceeds ............................     3
Selling Stockholders........................     4
Plan of Distribution .......................     5
Legal Matters ..............................     6
Incorporation of Certain Information
  by Reference..............................     6

===============================================================================

                                  4,338 Shares

                             Ionics, Incorporated

                                  4,338 Shares

                                  Common Stock

                                 ---------------

                                     REOFFER
                                    PROSPECTUS

                                 ---------------

                                  June 20, 2000

===============================================================================

                                       -9-
PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3.  Incorporation of Documents by Reference.

         The following  documents filed with the Commission are  incorporated by
reference in this Registration Statement:

         (a) The  Registrant's  Annual  Report on Form 10-K for the fiscal  year
ended December 31, 1999 filed  pursuant to the Securities  Exchange Act of 1934,
as amended,  which  contains  audited  financial  statements for the fiscal year
ended December 31, 1999.

         (b) The  Registrant's  Quarterly  Report  on Form  10-Q for the  fiscal
quarter ended March 31, 2000 filed  pursuant to the  Securities  Exchange Act of
1934, as amended,  which contains unaudited financial  statements for the fiscal
quarter ended March 31, 2000.

         (c) All other  documents  filed by the  Registrant  pursuant to Section
13(a) or 15(d) of the Securities Exchange Act of 1934, as amended, since the end
of the fiscal year covered by the annual report referred to in (a) above.

         (d) The  description  of the  Company's  Common Stock  contained in the
Company's Registration Statement on Form 8-A filed under the Securities Exchange
Act of 1934, as amended, pursuant to Section 12 thereof.

         All documents  subsequently  filed by the Company  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
hereby have been sold or which deregisters all securities then remaining unsold,
shall be deemed to be incorporated  by reference  herein and to be a part hereof
from the date of filing of such documents.

         Any  statement  contained  in a document  incorporated  or deemed to be
incorporated  by reference  herein shall be deemed to be modified or  superseded
for  purposes  of this  Registration  Statement  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  part of this  Registration
Statement.

Item 4.  Description of Securities.

      Not applicable.

Item 5.  Interests of Named Experts and Counsel.

      Certain  legal  matters in  connection  with the offering of the shares of
Common  Stock of the  Company  are being  passed upon for the Company by Stephen
Korn, Vice President,  General Counsel and Clerk of the Company. Mr. Korn is the
beneficial  owner of 90,086 shares of Common Stock,  including  88,000 presently
exercisable  stock options and 863 shares held in the Company's  Section  401(k)
Stock Savings Plan (based on January 31, 2000 plan data).

                                                                            -10-
Item 6.  Indemnification of Directors and Officers.

      The Company is permitted by Massachusetts  law and required by its By-laws
to indemnify any director or officer or former  director or officer  against all
expenses and liabilities  reasonably  incurred by such person in connection with
any  legal  action in which  such  person  is  involved  by reason of his or her
position with the Company  unless he or she shall have been finally  adjudicated
in any  action,  suit or  proceeding  not to have  acted  in good  faith  in the
reasonable  belief  that  his or her  action  was in the best  interests  of the
Company.  Such indemnification  shall include payment by the Company of expenses
incurred in defending a civil or criminal action or proceeding in advance of the
final  disposition  of such action,  or defending a civil or criminal  action or
proceeding,  upon  the  Company's  receipt  of the  undertaking  of  the  person
indemnified  to repay  such  payment if such  person  shall be  adjudicated  not
entitled to such indemnification.

      Directors  and  officers  are also  insured up to an  aggregate  amount of
$10,000,000 under Directors' and Officers'  liability and Company  Reimbursement
Policies.

      The  Company's  Restated  Articles  of  Organization  include a  provision
limiting the personal liability of a director of the Company to its stockholders
for  monetary  damages  for  breaches  of  their  fiduciary  duty to the  extent
permitted by the Massachusetts Business Corporation Law.

      See Item 9(c) for a statement  concerning  indemnification for liabilities
under the Securities Act of 1933.

Item 7.  Exemption for Registration Claimed.

      Not applicable.

Item 8.  Exhibits.

Exhibit No.        Description of Exhibit
-----------        ----------------------

4.1                Renewed Rights Agreement, dated as of August 19, 1997 between
                   Ionics, Incorporated and BankBoston N.A. (filed as Exhibit 1
                   to the Company's Current Report on Form 8-K dated August 27,
                   1997).

4.2                Form of Common Stock Certificate (filed as Exhibit 4.2 to the
                   Company's Annual Report on Form 10-K for the year ended
                   December 31, 1995).

4.3                Ionics,  Incorporated 1998 Non-Employee Directors' Fee Plan
                   (filed as Exhibit 10.1 to the Company's Quarterly Report on
                   Form 10-Q for the quarterly period ended September 30, 1998).

5                  Opinion of Stephen Korn, General Counsel.

23.1               Consent of Stephen Korn, General Counsel (included in Exhibit
                   5 hereto).

23.2               Consent of PricewaterhouseCoopers LLP.

24                 Power of Attorney.

                                                                            -11-
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 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;

                  (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.

                  (4) If the registrant is a foreign private issuer, to file a
                  post-effective amendment to the registration statement to
                  include any financial statements required by Rule 3-19 of this
                  chapter at the start of any delayed offering or throughout a
                  continuous offering.  Financial statements and information
                  otherwise required by Section 10(a)(3) of the Act need not
                  be furnished, provided, that the registrant includes in the
                  prospectus, by means of a post-effective amendment, financial
                  statements required pursuant to this paragraph (a)(4) and
                  other information necessary to ensure that all other
                  information in the prospectus is at least as current as the
                  date of those financial statements.  Notwithstanding the
                  foregoing, with respect to registration statements on Form
                  F-3, a post-effective amendment need not be filed to include
                  financial statements and information required by Section
                  10(a)(3) of the Act or Rule 3-19 of this chapter if such
                  financial statements and information are 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 Form F-3.

                                                                            -12-
(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 Section 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.

                                                                            -13-
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 Town of Watertown, in the Commonwealth of Massachusetts,  on
this 20th day of June, 2000.

                                        IONICS, INCORPORATED

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

         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.

                                         /s/ Arthur L. Goldstein
                                         -----------------------
Date:  June 20, 2000                     Arthur L. Goldstein,
                                         Chairman of the Board, President and
                                         Chief Executive Officer (principal
                                         executive officer) and Director

                                         /s/ Robert J. Halliday
                                         ----------------------
Date: June 20, 2000                      Robert J. Halliday,
                                         Executive Vice President, Chief
                                         Operating Officer and Chief
                                         Financial Officer (principal financial
                                         officer)

                                                                            -14-
Pursuant to the  requirements of the Securities Act of 1933,  this  Registration
Statement has been signed by the following  persons in the capacities and on the
dates indicated.

             SIGNATURE                 TITLE                       DATE

/s/ Douglas R. Brown                                           June 20, 2000
--------------------
Douglas R. Brown                      Director

--------------------
Stephen L. Brown                      Director

/s/ William L. Brown                                           June 20, 2000
--------------------
William L. Brown                      Director

/s/ Arnaud de Vitry d'Avaucourt                                June 20, 2000
-------------------------------
Arnaud de Vitry d'Avaucourt           Director

/s/ Kathleen F. Feldstein                                      June 20, 2000
-------------------------
Kathleen F. Feldstein                 Director

/s/ Arthur L. Goldstein               Chairman of the Board    June 20, 2000
-----------------------               and Director
Arthur L. Goldstein

/s/ William E. Katz                   Director                 June 20, 2000
-------------------
William E. Katz

                                      Director
------------------
William K. Reilly

/s/ John J. Shields                   Director                  June 20, 2000
-------------------
John J. Shields

/s/ Carl S. Sloane                    Director                  June 20, 2000
------------------
Carl S. Sloane

/s/ Daniel I. C. Wang                 Director                  June 20, 2000
---------------------
Daniel I. C. Wang

/s/ Mark S. Wrighton                  Director                  June 20, 2000
--------------------
Mark S. Wrighton

/s/ Allen S. Wyett                    Director                  June 20, 2000
------------------
Allen S. Wyett

                                                                            -15-
EXHIBIT INDEX

Exhibit No.        Description of Exhibit
-----------        ----------------------

4.1                Renewed Rights Agreement, dated as of August 19, 1997 between
                   Ionics, Incorporated and BankBoston N.A. (filed as Exhibit 1
                   to the Company's Current Report on Form 8-K dated August 27,
                   1997).

4.2                Form of Common Stock Certificate (filed as Exhibit 4.2 to the
                   Company's Annual Report on Form 10-K for the year ended
                   December 31, 1995).

4.3                Ionics,  Incorporated 1998 Non-Employee Directors' Fee
                   Plan (filed as Exhibit 10.1 to the Company's Quarterly
                   Report on Form  10-Q for the  quarterly  period  ended
                   September 30, 1998).

5                  Opinion of Stephen Korn, General Counsel            (p. 17)

23.1               Consent of Stephen Korn, General Counsel (included in Exhibit
                   5 hereto)                                           (p. 17)

23.2               Consent of PricewaterhouseCoopers LLP               (p. 18)

24                 Power of Attorney                                   (p. 19)

                                                                            -16-
EXHIBIT 5

                              Ionics, Incorporated

                                 65 Grove Street

                         Watertown, Massachusetts 02472

                                                              June 20, 2000
Ionics, Incorporated
65 Grove Street
Watertown, MA 02172

         Re:      Registration Statement on Form S-8 relating to the Ionics,
                  Incorporated 1998 Non-Employee Directors' Fee Plan
Gentlemen:

         As  General   Counsel  for  Ionics,   Incorporated,   a   Massachusetts
corporation  (the  "Company"),  I am familiar  with its  corporate  affairs.  In
particular,  I have acted as counsel  for the  Company  in  connection  with the
registration  of 100,000 shares of the Company's  common stock,  par value $1.00
per share (the "Shares"),  reserved for issuance under the Ionics,  Incorporated
1998 Non-Employee  Directors' Fee Plan (the "Plan"),  pursuant to a Registration
Statement on Form S-8 (the "Registration Statement") under the Securities Act of
1933,  as amended,  and the conduct of certain  corporate  proceedings  relating
thereto.

         As such counsel,  I have examined and am familiar with the Registration
Statement,  certain  corporate  records of the Company,  including  its Restated
Articles of Organization,  as amended,  its By-laws,  minutes of meetings of its
Board of Directors and stockholders,  and such other documents,  instruments and
certificates of government  officials as I have deemed  necessary as a basis for
the opinions herein expressed.

         In my examination described in the preceding paragraph,  I have assumed
the genuineness of all signatures,  the authenticity of all documents  submitted
to me as  originals,  the  conformity  to  the  corresponding  originals  of all
documents  submitted to me as copies,  the authenticity of the originals of such
copies, and the accuracy and completeness of all corporate records.

         I have made such  examination  of  Massachusetts  law as I have  deemed
relevant for purposes of this opinion,  but have not made any review of the laws
of any other  state or  jurisdiction.  Accordingly,  this  opinion is limited to
Massachusetts law.

         Based upon and subject to the  foregoing,  I am of the opinion that the
Shares to be issued by the Company  from time to time  pursuant to the Plan will
be duly authorized, validly issued, fully paid and non-assessable.

         I hereby  consent  to the  filing of this  opinion as an exhibit to the
Registration  Statement and to the reference to me in Item 5, Interests of Named
Experts  and  Counsel,  in the  Registration  Statement.  This  opinion is being
furnished to you solely for the foregoing use and, other than in connection with
such use, is not to be  disseminated,  reproduced or published in any form, used
for any other  purpose or relied upon by any other  person or entity  without my
prior written consent.

Very truly yours,

/s/Stephen Korn
---------------
Stephen Korn
General Counsel

                                                                            -17-
EXHIBIT 23.2

                       CONSENT OF INDEPENDENT ACCOUNTANTS

         We  hereby   consent  to  the   incorporation   by  reference  in  this
Registration  Statement  on Form S-8 of our report,  dated  February  22,  2000,
relating to the financial statements and financial statement schedule of Ionics,
Incorporated,  which appears in Ionics,  Incorporated Annual Report on Form 10-K
for the year ended December 31, 1999.

PricewaterhouseCoopers LLP
Boston, MA
June 19, 2000

                                                                            -18-
EXHIBIT 24

                                POWER OF ATTORNEY

         We, the  undersigned  Officers and  Directors of Ionics,  Incorporated,
hereby  severally  constitute  Arthur L.  Goldstein and Stephen Korn and each of
them to sign  for and in their  names in the  capacities  indicated  below,  the
Registration  Statement on Form S-8 dated June 20, 2000, herewith filed with the
Securities and Exchange  Commission,  and any and all amendments thereto for the
purpose of  registering  shares of Common Stock,  par value $1.00 per share,  of
Ionics, Incorporated, hereby ratifying and confirming our signatures as they may
be  signed  by our  attorneys  to such  Registration  Statement  and any and all
amendments to such Registration Statement.

         Witness our hands on the respective dates set forth below.
SIGNATURE                             TITLE                                DATE
             ---------                             -----                                ----
/s/ Arthur L. Goldstein       Chairman of the  Board,  Chief Executive Officer
-----------------------       and President (principal executive officer) and
Arthur L. Goldstein           Director                                              June 20, 2000

/s/ Douglas R. Brown

--------------------
Douglas R. Brown                      Director                                      June 20, 2000

----------------
Stephen L. Brown                      Director

/s/ William L. Brown
--------------------
William L. Brown                      Director                                      June 20, 2000

/s/ Arnaud de Vitry d'Avaucourt
-------------------------------
Arnaud de Vitry d'Avaucourt           Director                                      June 20, 2000

/s/ Kathleen F. Feldstein
-------------------------
Kathleen F. Feldstein                 Director                                      June 20, 2000

/s/ William E. Katz
-------------------
William E. Katz                       Director                                      June 20, 2000

-----------------
William K. Reilly                     Director

/s/ John J. Shields
-------------------
John J. Shields                       Director                                      June 20, 2000

/s/ Carl S. Sloane
------------------
Carl S. Sloane                        Director                                      June 20, 2000

/s/ Daniel I. C. Wang
---------------------
Daniel I.C. Wang                      Director                                      June 20, 2000

/s/ Mark S. Wrighton
--------------------
Mark S. Wrighton                      Director                                      June 20, 2000

/s/ Allen S. Wyett
------------------
Allen S. Wyett                        Director                                      June 20, 2000

                                                                            -19-