We used bilevel positive airway pressure ventilation (BiPAP; Respironics, Inc.) through a nasal mask to ventilate 57 consecutive, unselected patients with acute respiratory failure who were unresponsive to oxygen and medical therapy alone. We applied noninvasive positive pressure ventilation for almost 22 hours daily, with a median inspiratory positive airway pressure of 15 cm H2O (maximum, 20 cm H2O; minimum, 8 cm H (2O)) and a median expiratory positive airway pressure of 4 cm H2O (range, 8 cm H2O to 3 cm H2O). Seven patients had hypotension (systolic blood pressure <100 mm Hg; mean, 88 +/-6 mm Hg), 11 had radiologic and clinical findings of pulmonary edema, 20 had edema of the legs; 38 had tachycardia; 21 had hypertension; and 20 had arrhythmias. After 24 hours of BiPAP ventilation, only three patients with initial normal blood pressure and none of those with hypotension showed a decrease of 15 mm Hg or more in their mean blood pressure. None failed to respond to BiPAP. Of the 57 patients, 39 were successfully ventilated with BiPAP, and 18 patients required intubation or died.