The guiding rationale for the present study stemmed from the observations pertaining to a relatively high prevalence of obsessive compulsive disorder in Iran and the importance of psychotropic drugs in the initial treatment and management of these cases. In this context, the aim of this investigation was to compare the relative efficacy of clomipramine, fluoxetine and tranylcypromine in the symptomatic treatment of this disorder. Over a span of 3 years (1991-1994). A total number of 150 subjects were treateed by either one of the above mentioned drugs. Results indicate that fluoxetine (followed by clomipramine) was more effective in terms of speed and quality of efficacy on obsessive and compulsive symptoms and produced relatively lesser adverse side effects than tranylcypromine. Tranylcypromine was not very effective in the tratement of obsessive compulsive symptoms.