The hypothalamic-pituitary function of 93 children, who had received central nervous system (CNS) prophylaxis as part of their therapy for acute lymphocytic leukemia (ALL), and who remained in continuous complete remission, was evaluated retrospectively. Treatment regimens included--Group I: 31 subjects, intrathecal methotrexate (IT MTX); Group II: 31 subjects, IT MTX plus 2400 rad cranial irradiation; and Group III: 31 subjects, IT MTX and intravenous intermediate-dose methotrexate. Serum thyroid-stimulating hormone (TSH) and T4 levels were normal. All participants had normal adrenocorticotropic hormone (ACTH) secretion as assessed by plasma cortisol responses to insulin hypoglycemia. Urinary follicle-stimulating hormone (FSH) and luteinizing hormone (LH) excretion of pubertal and postpubertal patients (N = 37) was appropriate, except for one subject from Group I who had an abnormally high output of gonadotropins, and one from Group II who had abnormally low levels. Growth hormone (GH) responses were subnormal after sequential arginine-insulin stimulation as follows--Group 1: 3 of 31 patients; Group II: 6 of 25 patients; and Group III: 2 of 29 patients. Nevertheless, all children had normal linear growth. It was concluded that the three forms of CNS prophylaxis evaluated had no long-term adverse effect on TSH and ACTH secretion. FSH-LH production appears to be normal, but final judgment must await follow-up studies because 60% of the patients were prepuberteral or still receiving chemotherapy. Eleven patients had subnormal GH responses after pharmacologic stimulation of the pituitary, but long-term linear growth was unaffected.