In a 9-week open label study, seven outpatients with obsessive-compulsive disorder were treated with fluoxetine, a selective inhibitor of neuronal reuptake of serotonin. After a 7-day placebo washout period, patients were given a dose of 40 mg/day, which was gradually increased to a maximum of 80 mg/day. 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 serotonergic antidepressants may be useful in the treatment of obsessive-compulsive disorder and underline the need to carry out double-blind clinical trials to confirm these results.