Recent studies suggest that noninvasive positive pressure ventilation (NPPV) administered by nasal or oronasal mask avoids the need for endotracheal intubation, rapidly improves vital signs, gas exchange, and sense of dyspnea, and may reduce mortality in selected patients with acute respiratory failure, but few controlled trials have been done. The present study used a randomized prospective design to evaluate the possible benefits of NPPV plus standard therapy versus standard therapy alone in patients with acute respiratory failure. Patients to receive NPPV were comfortably fitted with a standard nasal mask connected to a BiPAP ventilatory assist device (Respironics, Inc., Murrysville, PA) in the patient flow-triggered/time-triggered (S/T) mode, and standard therapy consisted of all other treatments deemed necessary by the primary physician, including endotracheal intubation. The need for intubation was reduced from 73% in the standard therapy group (11 of 15 patients) to 31% in the NPPV group (5 of 16 patients, p < 0.05). Among chronic obstructive pulmonary disease (COPD) patients, the reduction was even more striking, with 8 of 12 (67%) control patients requiring intubation compared with 1 of 11 (9%) NPPV patients (p < 0.05). Heart and respiratory rates were significantly lower in the NPPV group than in control patients within 1 h, and PaO2 was significantly improved in the NPPV group for the first 6 h. Dyspnea scores and maximal inspiratory pressures were better in the NPPV than in control patients at 6 h, and nurses and therapists spent similar amounts of time at the bedside for both groups.(ABSTRACT TRUNCATED AT 250 WORDS)