The present experiment was performed to examine the role of serotonergic mechanisms in the control of copulation and the post-ejaculatory refractory period in the male rat. Disruption of central serotonergic systems in two separate groups of animals was achieved by: (1) selective electrolytic lesions of the midbrain raphe nuclei, or (2) localized intraventricular or intracerebral injection of a specific serotonergic neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT). A third group of animals was tested for sexual behavior following intraperitoneal injection of p-chlorophenylalanine (PCPA), an inhibitor of serotonin synthesis. Both electrolytic and neurochemical lesions localized in the dorsal raphe nucleus produced a highly significant shortening of the ejaculatory latency, and the post-ejaculatory refractory period. Disruption of serotonergic mechanisms following intraventricular injection of 5,7-DHT or systemic administration of PCPA also caused a significant reduction in the length of the refractory period. These results support the hypothesis that central serotonergic systems are normally inhibitory to certain facets of male copulatory behavior and suggest the existence of a serotonergic control system which normally exerts an inhibitory influence over the resumption of mating following ejaculation.