EXHIBIT 11
                                  IONICS, INCORPORATED

                           COMPUTATION OF EARNINGS PER COMMON
                               AND COMMON EQUIVALENT SHARE

                                                       

                                                      YEARS ENDED DECEMBER 31          

                                                1994            1993            1992      
                                                                    
Net Income                                   $15,448,000     $13,807,000     $12,820,000

Calculation of primary earnings per
common and common equivalent share:

Weighted average common shares outstanding    13,926,000      13,870,000      13,512,000

Increase from assumed exercise of 
stock options and investment of pro-
ceeds in treasury stock, based upon
average market prices                            272,000         250,000         326,000

Weighted average number of common and 
common equivalent shares outstanding          14,198,000      14,120,000      13,838,000

Earnings per common and common
equivalent share                                   $1.09           $ .98           $ .93


Calculation of fully diluted earnings per
common and common equivalent share: 

Weighted average common and common equivalent
shares outstanding used in calculation
of primary earnings per common and
common equivalent share                       14,198,000      14,120,000      13,838,000

Increase from assumed exercise of stock
options and investment of proceeds in
treasury stock, based upon year-end
market price                                      42,000           8,000          24,000

Weighted average number of common and
common equivalent shares used to calculate
fully diluted earnings per common and 
common equivalent share                       14,240,000      14,128,000      13,862,000

Earnings per common and common
equivalent share assuming full dilution            $1.08(A)        $ .98           $ .92(A)


(A) Dilution is less than 3% so the primary
    basis was used for per share calculations.

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