Tricyclic antidepressant clomipramine or selective serotonin reuptake inhibitors (SSRIs) have been commonly used for the treatment of premature ejaculation. In the present study, we analyzed the concentrations of serotonin and 5-hydroxyindoleacetic acid (5-HIAA) in the medial preoptic area (MPOA) of the hypothalamus by awakening animal microdialysis following administration of clomipramine and various SSRIs. We then compared the serotonin metabolism and clinical effects of clomipramine and SSRIs on premature ejaculation. Basal extracellular serotonin level in the MPOA was higher than other brain regions and it was significantly increased by clomipramine and the SSRIs. The rank order of the concentration of serotonin at the MPOA was clomipramine, sertraline, paroxetine and fluoxetine and the concentrations of 5-HIAA was vice versa. The changes in serotonin concentration at the MPOA appeared closely associated with the clinical effects of these drugs on premature ejaculation. These results suggest that the serotonergic neuronal activity in the MPOA may have an selective inhibitory influence on ejaculation, and the effects of clomipramine and SSRIs on erectile function are mainly mediated by MPOA of the hypothalamus.