The effect of adjunctive fluoxetine on negative schizophrenic symptoms was evaluated in 34 chronic schizophrenic in-patients on maintenance therapy with neuroleptics. They received randomly, on a double-blind basis, fluoxetine (20 mg/day) or placebo for 12 weeks. In the fluoxetine group, three patients dropped out because of side effects. Negative symptoms, as measured by change on the Scale for Assessment of Negative Symptoms at the end point compared to baseline values, were significantly improved in fluoxetine-treated patients (p < 0.001), but not in the placebo group. Fluoxetine treatment did not influence positive schizophrenic symptoms, while it induced a slight, but statistically significant, decrease (p < 0.05) in depressive symptoms, as measured by the Hamilton Rating Scale for Depression. Unwanted effects were more common among patients receiving fluoxetine. These data suggest that the addition of fluoxetine to neuroleptic treatment may be beneficial in some schizophrenic patients with negative symptoms.