A large body of literature, including six randomized studies, supports applying noninvasive positive-pressure ventilation via mask in patients with chronic obstructive pulmonary disease and acute respiratory failure as an early intervention to prevent deterioration to the point of requiring endotracheal intubation or as an alternative to endotracheal intubation in those with the most severe impairment in gas exchange. Correctly applying noninvasive positive-pressure ventilation results in rapid improvement in the pathophysiology of acute respiratory failure and correction of arterial blood gas abnormalities. A reduction in Pco2or an increase in pH within 1 to 2 hours of noninvasive positive-pressure ventilation predicts a sustained improvement in gas exchange and shorter duration of ventilatory support. Under adequate monitoring, the risk of postponing endotracheal intubation in patients in whom noninvasive positive-pressure ventilation fails (20% to 30%) is minimal.