The 5-hydroxytryptamine (5-HT) reuptake inhibitors zimelidine (10 mg/kg IP 1.5h pretest) or alaproclate (20 mg/kg IP 1.5h pretest) produced a prolongation of the ejaculation latency and of the post-ejaculatory interval in male rats treated with a subthreshold dose of 5-hydroxytryptophan (5-htp) (12.5 mg/kg IP 1h pretest). The 5-HTP-induced (50 mg/kg IP 1h pretest) prolongation of ejaculatory latency was effectively counteracted by administration of the 5-HT receptor blocking agent metergoline (1 mg/kg IP 1.5h pretest). All animals were treated with an inhibitor of peripheral aromatic amino acid decarboxylase, indicating that the effects are of central origin. The results support the contention that central 5-HT plays an inhibitory role in male rat sexual behavior.