The pulse oximeter was evaluated for use in neonates in the delivery room. One hundred neonates, delivered vaginally or by Caesarean section with general or epidural anaesthesia, were studied. After delivery, pulse oximetry probes were placed simultaneously on the ulnar side of the right hand and on the right Achilles tendon to determine whether there was a difference in arterial oxygenation (SpO2). Measurements of SpO2 were taken at 1, 5, 10 min, and 24 hr after delivery. At one and five minutes, SpO2 recorded from the right hand was higher than that recorded from the lower extremities (71.9% +/- 6.5% vs 63.4% +/- 4.3% and 83.3% +/- 4.2% vs 76% +/- 4.1%, mean +/- SD, respectively). At ten minutes these differences diminished, and had almost completely disappeared after 24 hr. These results can be explained by the presence of R-L shunting at the ductus arteriosus level, producing reduced SaO2 in the lower extremities. Oxygen saturation did not differ between neonates delivered vaginally or by Caesarean section, regardless of the presence or type of anaesthesia. We concluded that neonates remain relatively desaturated in the immediate postpartum period and that the SpO2 obtained from the right hand is a better index of neonatal oxygenation than that obtained from the heel.