Plasma ACTH was measured by radioimmunoassay including preliminary extraction onto adsorbent glass particles. Normal basal values for children 4-16 years of age were 11-82 microgram/ml, corresponding to values found in the literature. Normal values were found in girls with precocious puberty, children with McCune-Albright and Beckwith-Wiedemann's syndrome. Values between 233 and 305 pg/ml were found in untreated children with congenital adrenal hyperplasia. In primary Addison's disease, very high levels (654-1 413 pg/ml) before cortisone therapy and their decline to nearly normal values during therapy are described. ACTH values in a case of pituitary Cushing's syndrome was just above the normal range (104-163 microgram/ml).