Hypothalamic-pituitary function was studied in 4 patients with anorexia nervosa of different degree of severity before and after refeeding. Gonadotrophin secretion was low in all subjects and improved in two after a prolonged period of feeding. In one subject there was a failure of pituitary gonadotrophin secretion after the administration of hypothalamic gonadotrophin-releasing hormone but the response was restored to normal after treatment. Thyroid function was reduced in one patient only but returned to normal after intravenous therapy for 6 days. Growth hormone and cortisol levels were elevated in all patients, and in one severe case the growth hormone values were extremely high. There was also a disturbance of the hypothalamic control of growth hormone and pituitary-adrenal function, which returned to normal after refeeding. One patient with severe hypothermia was resistant to the administration of a pyrogen, but developed a normal febrile response after treatment.