In 20 patients with congenital brain disorders, the influence of the CNS maldevelopment on the neuroendocrine system was investigated by assessment of the hypothalamic-pituitary function through measurements of the secretory reserve of pituitary hormones (GH, PRL, TSH, LH and FSH) in response to injections of insulin, TRH and LH-RH, and of the secretion of sleep-dependent pituitary hormones with polygraphic recording. The subjects consisted of 9 patients with midline anomalies of the brain and face, 3 patients with hydrocephalus, hydroencephalodysplasia or microcephalus, and 8 patients with the malformation syndrome associated with mental retardation. Ten of the 18 patients examined showed normal responses of GH secretion in the loading test (secretory peaks: greater than 10 ng/ml). But only 4 of these patients were found normal in respect of GH secretory peaks of more than 10 ng/ml during sleep. Of these 17 children, 5 showed abnormal values for basal secretion of PRL, and/or the secretory peak of PRL on injection of TRH. Two children showed hypersecretion of PRL during sleep. One patient out of the 19 examined was unresponsive in gonadotropin secretion to injection of LH-RH and 2 patients displayed excessive responses. During sleep, 4 of the 13 patients studied were found to be hypersecretory and 2 hyposecretory of gonadotropin. These results suggest that abnormalities in pituitary hormone secretion are frequently present in patients with CNS maldevelopment, and growth disturbances and abnormal sexual development may in some instances be due to endocrine abnormalities.