Seven patients who met DSM-III-R criteria for obsessive compulsive disorder and had only a partial response to the serotonin reuptake blockers fluoxetine, fluvoxamine, or clomipramine or were unable to tolerate therapeutic doses of these agents due to side effects underwent open treatment with fenfluramine augmentation. Fenfluramine is a serotonin releaser and reuptake blocker which is marketed as an anorectic agent. In doses of 20 to 60 mg/day, fenfluramine augmentation was well tolerated and resulted in a further decrease in obsessions and compulsions in six of these patients. Larger controlled studies are needed to confirm this finding.