Plasma immunoreactive glucagon, as well as insulin and glucose levels, was measured in 62 women and their infants following a term gestation vaginal delivery. Simultaneously obtained samples were drawn from the maternal antecubital vein (MV), umbilical vein (UV), and umbilical artery (UA). Forty-seven of these subjects were untreated (control) and 15 had received a maternal intravenous injection of 1 mg of glucagon within 40 minutes of delivery. It was shown that the umbilical cord glucagon levels were not different from the maternal levels in the control subjects (mean MU, 181.0; UU, 191.9; UA, 161.0 pg/ml). There was no correlation between the maternal and umbilical glucagon levels or the UV glucagon levels and the insulin or glucose concentrations. Neither the fetal sex, placental weight, or infant weight were correlated with the MV or UV glucagon concentration. Following the glucagon injection, the maternal plasma glucagon levels rose significantly, whereas the umbilical blood values did not change. These results suggest that glucagon does not significantly pass through the human term placenta.