Carbohydrate metabolism was studied in nine growth hormone-deficient children before and one year after treatment with human growth hormone (HGH). Before treatment the mean plasma immunoreactive insulin concentrations following administration of glucose and tolbutamide were significantly reduced. After one year of HGH therapy the mean plasma immunoreactive insulin levels in response to glucose and tolbutamide were greater than before treatment. The pattern of response of plasma free fatty acids, which was abnormal before treatment, returned to normal with therapy. The improvement in insulin responsiveness following HGH suggests that in the absence of growth hormone pancreatic beta cells have a decreased capacity to release insulin which improves following therapy. The effect of HGH on growth may be due, in part, to its insulinogenic activity.