In a 9-week open-label study, 7 outpatients with obsessive compulsive disorder were treated with fluoxetine, a selective inhibitor of neuronal reuptake of serotonin. A significant improvement was found in the symptomatology of patients as measured on the obsessive compulsive subscale of the Comprehensive Psychopathological Rating Scale (p less than 0.001) and the Clinical Global Impression of severity of illness (p less than 0.01). These findings support the hypothesis that serotoninergic antidepressants may be useful in the treatment of obsessive compulsive disorder.