Cortisol and growth hormone (GH) secretion (spontaneous variations at night and the release induced by insulin hypoglycaemia) were investigated in 69 children and adolescents. Statistical analysis of approximately 600 pairs of cortisol and GH values in this study demonstrated that physiological fluctuations of cortisol do not alter GH secretion. A review of the literature shows that GH secretion is consistently depressed in Cushing's disease of central origin and in Cushing's syndrome due to adrenal carcinoma. When acutely administered, doses higher than 100 mg of cortisol (or equivalent amounts of other steroids) per adult are necessary to block GH secretion and the hormones have to be given several hours previously. In long-term steroid treatment, suppression of GH is observed in only 1 out of 3 patients. The effect apparently does not persist beyond elimination of the last dose, i.e. generally not longer than 12 to 24 h. These data can be taken as a rationale for intermittent or alternating dosage schedules, and for the use of short acting derivatives if long-term, high-dose steroid treatment is necessary in children. It remains to be established whether growth deficiency in exogenous hypercortisolism is due to suppression of GH secretion, decreased production of somatomedins, direct antagonism of the action of somatomedins on growing cartilage, or a combination of these mechanisms.