Unexpected stability of arterial oxygen and carbon dioxide tensions occurred in infants recovering from respiratory distress syndrome (RDS) on the abrupt withdrawal of CPAP at 6 cmH2O pressure. 30 preterm infants (birthweights 880--3200 g gestational ages 29--38 weeks) were treated at a mean age of 10 hours and for a mean duration of 62 hours. CPAP was stopped when F1O2 requirement fell below 0.3, and stable PO2 was maintained for 4 hours. Discontinuation of CPAP at 6 cmH2O resulted in a mean change in PO2 from 66 to 64 mmHg (8.8 to 8.5 kPa) and a mean change in PCO2 from 41 to 40 mmHg (5.4 to 5.3 kPa). We conclude that this population of infants suffering from moderate RDS tolerated the abrupt withdrawal of CPAP, and that gradual reduction of pressure was unnecessary.