In young male subjects peripherally administered growth hormone-releasing hormone (GHRH) enhances GH and slow wave sleep (SWS) and blunts cortisol. In contrast, in a sample of females 19-76-year old, GHRH impairs sleep and enhances adrenocorticotropic hormone (ACTH) and cortisol. In the latter study, the days of investigation were not adapted to the menstrual cycle and premenopausal and postmenopausal women as well were included. Placebo and GHRH were given during consecutive nights. In order to confirm or reject the sexual dimorphism of the effects of GHRH on sleep we applied an improved study design. In the present study we examined the effect of pulsatile administration of two dosages of GHRH (4x25 or 4x50 microg intravenously, respectively) on sleep electroencephalogram (EEG) and nocturnal hormone secretion in healthy young women according to a randomized schedule. To rule out the influence of gonadal hormone activity, the study was adapted to the phase of the menstrual cycle and was performed at 4-6th day of menstrual cycle. A carry-over effect was excluded by the interval of at least 4 weeks between examinations. Compared to placebo rapid-eye-movement sleep decreased during the first half of the night after 4x25 microg GHRH and sleep stage 4 decreased after 4x50 microg GHRH. After both dosages GH increased whereas ACTH and cortisol remained unchanged. This study confirms that systemic GHRH impairs sleep in women.