Plasma growth hormone responses to insulin-induced hypoglycemia were examined in eight preschool-age autistic children. Six of these children were examined on two separate occasions: during the period of baseline evaluation and after 4 weeks of daily haloperidol administration. On at least one occasion, half of this small sample exhibited persistent elevation of growth hormone levels, with a failure to return to baseline values over the course of a 135-minute period postinsulin infusion. These data are consistent with the occurrence of hypothalamic dysfunction in subgroups of autistic children. Short-term administration of haloperidol did not diminish the ability of the pituitary to secrete growth hormone in response to insulin-induced hypoglycemia.