Infants with IRDS were treated with CPAP early (0.40 FIO2; WITH PaO2 less than 60 mm Hg) or late (0.70 FIO2; with PaO2 less than 60 mm Hg). There was no difference in survival, duration of CPAP therapy, total time of oxygen administration, or complications. The early treated infants needed a lower FIO2 (maximum 0.55) and had a less severe clinical course. The late treated infants were subjected to 0.70 or more FIO2 for an average of 24 hours and were in greater than 0.40 FIO2 significantly longer than those given CPAP early. Infants who weighed less than 1,500 gm and had severe disease did not do well regardless of when CPAP was applied.