The role of raphe nuclei in the sleep-watch cycle and in the mechanism of analgesia is pointed out here. Though the importance of the aforesaid nuclei in sleep genesis is evidenced by several studies, the regulating mechanism of sleep appears to be still obscure. The sleep theory still shows several inconsistencies when critically examined, and appears to be rather incomplete in its formulation. The role of raphe nuclei is far clearer in what regards pain control. According to most studies a nociceptive impulse control is exerted by serotoninergic raphe neurons acting on interneurons at the spinal posterior process level.