The process of aging is characterized by a disturbed neuroendocrine regulation, including a changed secretory activity of the hypothalamo-pituitary-adrenocortical (HPA) axis. In the present study adrenocorticotropin (ACTH) and cortisol secretion was monitored during nocturnal sleep (controlled by somnopolygraphy) in healthy aged men (N = 10, aged range 70-92 years, mean 78.2 years) and women (N = 10, age range 70-88 years, mean 78.6 years), and in young male controls (N = 16, age range 20-34 years, mean 24.9 years). Blood was drawn every 15 min. Most important, basal HPA secretory activity was enhanced distinctly in the elderly, as indicated by significantly elevated nadirs of plasma cortisol and ACTH concentrations occurring during early nocturnal sleep (p < 0.001, compared to young controls) and by elevated average levels of cortisol and ACTH between 23.00 and 03.00 h (p < 0.001). The first rise in nocturnal plasma cortisol began, on average, 67 min earlier than in young controls (p < 0.005). Changes of endocrine activity were associated with marked reductions of slow-wave sleep (SWS, p < 0.05) and rapid eye movement (REM) sleep in the elderly (p < 0.01), while time awake and in stage 1 sleep was increased. The REM sleep coincided with decreased HPA secretory activity, irrespective of age, indicating that the link between the ultradian sleep structure and the secretory HPA activity is maintained in the elderly.(ABSTRACT TRUNCATED AT 250 WORDS)