The mean plasma pancreatic glucagon level at birth in 44 normal infants delivered vaginally was 140 pg/ml. The simultaneous maternal level was 122 pg/ml which was not quite significantly different at the P [unk]0.05 level. 2 hours after birth 30 of these infants had a mean rise in plasma glucagon of 51 pg/ml (P [unk] 0.01), and their mothers had a fall of 38 pg/ml (P [unk] 0.05). The mean plasma pancreatic glucagon level at birth in 12 normal infants delivered by caesarean section was 130 pg/ml which did not differ significantly from the group delivered vaginally. The glucagon level at birth in 20 infants with fetal distress (fetal scalp pH [unk] 7.2 or umbilical artery pH [unk] 7.15) was 244 pg/ml, and this was significantly higher than for normal infants at birth (P [unk] 0.01). Whereas the rise in neonatal glucagon 2 hours after birth might have been caused by a mean fall in blood glucose of 23 mg/100 ml, the infants with fetal distress had normal glucose levels, so that another mechanism must be responsible for their raised glucagon.