To assess whether neuroendocrine dysfunction is present in children with acquired immunodeficiency syndrome (AIDS) and growth failure, we evaluated the thyroid, adrenal, and growth hormone-insulin-like growth factor I (IGF-1) axes in nine children with AIDS and failure to thrive. Basal thyroid-stimulating hormone, free thyroxine, and triiodothyronine levels were normal in eight of the nine children and indicated primary hypothyroidism in one child; thyroxine levels were elevated in four and normal in five children. Thyroxine-binding globulin levels were elevated in all children. Serial measurements of thyroid-stimulating hormone, made hourly from 2 to 6 pm and from 10 pm to 2 am, revealed a flat diurnal rhythm of thyroid-stimulating hormone in six children, which may indicate early central hypothyroidism, and a normal nocturnal rise in the remaining three children. Basal plasma corticotropin and aldosterone levels were normal in all children, plasma renin levels were normal in three and elevated in six children, and cortisol levels were normal or elevated in all children. Corticotropin-stimulated cortisol levels exceeded 500 nmol/L (18 micrograms/dl) in all children except one, who was receiving treatment with ketoconazole. Thus adrenocortical function appeared to be grossly intact. The peak growth hormone responses to provocative testing was normal (greater than 7 ng/ml) in eight children and low in one child. The plasma level of insulin-like growth factor I was normal in eight of the nine children and low in one child. We conclude that growth failure in children with AIDS does not usually result from a recognized endocrine cause and that adrenal function is usually normal. However, endocrine deficiency may contribute to morbidity in some children with AIDS.