The efficacy and safety of fluoxetine were compared with those of imipramine and of placebo in a 6-week randomized double-blind parallel study of patients with major depressive illness. Mean values for all efficacy measurements were improved over baseline with fluoxetine and imipramine treatment (p less than .001). More fluoxetine patients completed the study than did imipramine or placebo patients. Predominant adverse experiences reported by imipramine patients were dry mouth and dizziness/lightheadedness. Predominant adverse experiences reported by fluoxetine patients were drowsiness/sedation and excessive sweating. In a subsequent 48-week open-label study, the predominant adverse experience in the fluoxetine group was excessive sweating and in the imipramine group was still dry mouth. In this study, fluoxetine relieved the symptoms of major depressive illness effectively and significantly better than placebo and was better tolerated than imipramine.