Maternal and fetal blood glucose and insulin levels were studied in 10 women in the second stage of labor after administration of terbutaline, 250 micrograms intravenously. The transport of the drug across the placenta was also studied. Saline solution was administered to four other women who served as controls. A rise in maternal plasma insulin levels occurred in all patients but was more pronounced in patients treated with terbutaline less than 25 minutes before delivery than in those treated more than 45 minutes prior to delivery. No difference was found in maternal blood glucose levels between terbutaline-treated patients and controls. Blood glucose increased in the fetuses during the second stage of labor and paralleled that of the mothers, but on a lower level. None of the newborn infants demonstrated hypoglycemia during the first 90 minutes after birth. Terbutaline crossed the placenta rapidly, and fetal plasma levels up to 55% of the maternal plasma levels were found. The conclusion is that this form of administration of terbutaline does not seem to have any negative short-term influences on the fetal carbohydrate metabolism.