Fluoxetine hydrochloride, a specific inhibitor of serotonin reuptake, was given orally to five adult males to study its effect on fasting and insulin-stimulated release of PRL. A 3-day course of fluoxetine (30 mg daily) had no demonstrable effect on fasting PRL levels. Fluoxetine significantly enhanced insulin-induced PRL release. These data suggest that serotoninergic pathways have little or no part in the control of spontaneous PRL secretion in man, whereas they may play a role in insulin-stimulated PRL release.