Fluoxetine hydrochloride, a new antidepressant, was administered to 10 obsessive-compulsive patients, and the effects of treatment were examined in a single-blind placebo design. The effects of fluoxetine were examined with respect to depressive symptomatology and obsessions and compulsions per se. The results suggest that fluoxetine affected depressive symptoms but also had an effect on self-reported measures of obsessions and ritualistic behavior. Results are discussed in terms of improvement in obsessive-compulsive disorder, the relation of improvement to initial levels of depression, and patients' ability to tolerate the drug.