The authors studied the use of CPAP by face mask in 44 patients with mild to moderate acute respiratory insufficiency (mean PaO2/FIO2 = 171 +/- 42 (SD). All patients improved their oxygenation (mean PaO2/FIO2 = 300 +/- 68 (SD) after the application of CPAP (mean 9 +/- 3 (SD) cm H2O). One patient developed a respiratory acidemia and was intubated. No other significant complications or adverse side effects occurred. The authors conclude that CPAP by face mask in a select group of patients will improve lung function and arterial oxygenation without the use of tracheal intubation and mechanical ventilation.