Twenty preterm infants in respiratory distress, each with an umbilical catheter in place, were studied during their first 24 h of hospitalization, to determine the effects of continuous transcutaneous oxygen (PtcO2) monitoring on the frequency of arterial blood gas (ABG) determinations and on the incidence of hypoxia and hyperoxia. PtcO2 was measured continuously in all infants during the 24-h period. By random allocation, PtcO2 data were withheld during either the 1st or 2nd 12-h period of hospitalization from clinicians caring for the infant. Comparison of the 12-h period in which PtcO2 data were available (open TcM) with the period in which they were withheld showed no difference in the number of ABG determinations (6.3 +/- 0.6 vs 7.4 +/- 1.0/12 h). During the open TcM period, there was significantly less hypoxia (PtcO2 less than 50 torr) (9.0 +/- 3.7% vs 16.3 +/- 4.2%, p less than .025) but no difference in hyperoxia (PtcO2 greater than 100 torr). Although continuous PtcO2 monitoring in acutely ill newborns did not decrease the frequency of ABG determinations, it may lessen morbidity by decreasing the amount of hypoxia infants experience while being stabilized early in hospitalization.