Because T-piece breathing may impair oxygenation, the best airway pressure from which to extubate ventilated patients is controversial. We compared the effects of extubation after 1 h of either CPAP 5 and T-piece/ZEEP. Once weaned from mechanical ventilation and breathing spontaneously, 106 patients were randomized to 1 h CPAP or 1 h T-piece/ZEEP, following which patients were extubated and mask O2 administered. No significant difference existed between groups in age, sex, HR, BP, FIO2, PaCO2 or PaO2. However, P(A-a)O2 was significantly greater at 120 min in the CPAP group. Within the CPAP group, P(A-a)O2 was also significantly worse at 120 vs 0 min. Nineteen T-piece patients showed improved P(A-a)O2 at 120 min compared with only ten CPAP patients. Three CPAP and two T-piece patients subsequently required reintubation. This study demonstrates that use of a T-piece dose not impair arterial oxygenation and may in fact be superior to direct extubation from CPAP 5.