PIP: Oxygen is the most liberally and often used medication in any neonatal unit. Appropriate oxygen therapy has resulted in improved neonatal survival and a reduction in oxygen-related morbidity over the past 2 decades. However, the degree of arterial oxygenation needs to be continuously and precisely monitored when managing critically ill neonates in order to prevent the adverse effects of both hypoxia and hyperoxia. The authors measured the extent of hyperoxia in spontaneously breathing neonates receiving supplemental oxygen by hood and the utility of pulse oximeters in detecting hyperoxia in newborn infants. The study was conducted during January-April 1996 among 63 preterm and 60 term babies admitted to the Neonatal Unit of Kalawati Saran Children's Hospital, who required supplemental oxygen by hood. All of the infants were independently evaluated by an observer after initial stabilization of temperature and perfusion. 91% of spontaneously breathing infants receiving supplemental oxygen by hood were hyperoxemic, with no relation to the type of morbidity for which oxygen therapy was indicated.