Narcolepsy, a disorder which is clinically characterized by recurring episodes of sleep during the day, frequently associated with nocturnal disrupted sleep and polygraphically by sleep onset REM periods, has been studied in regard to the relationships between GH, cortisol secretion and sleep. Ten narcoleptics were polygraphically recorded during 24 h after one night's adaptation. Blood samples were taken every 20 min for GH and cortisol immuno-assays. Three narcoleptics were recorded twice 2 months later and 2 normal subjects served as controls. The following results were obtained: GH secretory pattern was different in narcoleptics and controls; two groups were identified: the first one showed a very low basal GH secretion with rare and small secretory peaks not clearly linked with sleep. One subject of this group recorded twice showed a similar pattern. The second group exhibited a higher basal secretion with many peaks without any well-defined relationship to sleep stages. The pattern was again consistent in two recordings of 2 subjects in this group. Furthermore GH secretion rose significantly (p less than 0.01) between 2100 and 0000 with no apparent relationship to sleep stages. The cortisol secretory pattern showed a significant rise (p less than 0.01) between 0400 and 1000 and was not different in narcoleptics and controls. In narcolepsy the monophasic sleep-wakefulness cycle is disrupted. The GH secretion pattern is modified whereas the circadian pattern of cortisol secretion is normal and independent of the sleep-wakefulness cycle of the narcoleptic patient.