<PAGE>

                                    EXHIBIT 11.1
                                           
                            TRIANGLE PHARMACEUTICALS, INC.
                            (A DEVELOPMENT STAGE COMPANY) 
          COMPUTATION OF NET LOSS PER SHARE AND PRO FORMA NET LOSS PER SHARE
                                     (UNAUDITED)
                                           
<TABLE>
                                    THREE MONTHS    NINE MONTHS     THREE MONTHS    NINE MONTHS
                                       ENDED           ENDED           ENDED           ENDED
                                    SEPTEMBER 30,   SEPTEMBER 30,   SEPTEMBER 30,   SEPTEMBER 30, 
                                    -------------   -------------   -------------   -------------
                                      1996 (1)        1996 (1)        1997 (2)        1997 (2) 
                                    -------------   -------------   -------------   -------------
<S>                                 <C>             <C>             <C>             <C>     
Historical weighted average 
 shares...........................                                    19,988,451     18,554,524
Pro forma historical weighted 
average shares outstanding........    4,107,643       4,925,945               --             --
 Series A preferred stock, 
 convertible to Common Stock at   
 consummation of the initial 
 public offering..................    5,231,671       5,231,671               --             --
Series B preferred stock, 
 convertible to Common Stock at 
 consummation of the initial 
 public offering..................    3,706,234       3,706,234               --             --
Common stock equivalents for 
 preferred stock warrants 
 outstanding......................           --              --               --             --
Common stock equivalents for 
 options outstanding..............           --              --               --             --
                                    -----------     -----------     ------------   ------------
Shares used in computing pro 
 forma net loss per share.........   13,045,548      13,863,850       19,988,451     18,554,524
                                    -----------     -----------     ------------   ------------
                                    -----------     -----------     ------------   ------------

Net Loss..........................  $(2,538,859)    $(8,038,277)    $(18,214,006)  $(27,374,905)
                                    -----------     -----------     ------------   ------------
                                    -----------     -----------     ------------   ------------

Pro forma net loss per share......  $     (0.19)    $     (0.58)    $      (0.91)  $      (1.48)
                                    -----------     -----------     ------------   ------------
                                    -----------     -----------     ------------   ------------
</TABLE>

    (1)  Weighted average common stock outstanding during the period including
         all common stock issued at prices below the public offering price
         during the twelve month period preceding the offering as if it was
         outstanding at inception (July 12, 1995).  Issuance of convertible
         preferred stock, preferred stock warrants and common stock options at
         prices below the public offering price during the twelve month period
         preceding the offering have been included as common stock equivalent
         as if they had been issued as common stock as of July 12, 1995.

    (2)  The weighted average shares outstanding used in the calculation of net
         loss per share do not include common stock equivalents because they
         have the effect of reducing net loss per share.