We used noninvasive positive-pressure ventilation to treat hypercapnea due to acute exacerbations of chronic respiratory failure (21 episodes in 19 patients; COPD, 4; pulmonary tuberculosis sequelae, 4; silicosis, 3; silicotuberculosis, 3; bronchiectasis, 3; others, 2). All patients had acute onsets of severe hypercapnea (PaCO2 > 45 Torr), acute decreases in pH (< 7.35), and tachypnea, paradoxical breathing or both. During the first 2 to 4 hours of bi-level positive airway pressure, PaCO2 decreased from 72 to 61 Torr (p < 0.0005), pH increased from 7.26 to 7.31 (p < 0.001), and respiratory rate decreased from 30 to 25 breaths/min (p < 0.005). In three cases leakage of air through the mouth prevented improvement in the patients' conditions, but in two of those a face mask was then used successfully. In 17 of the 21 episodes (81%) gas exchange improved and intubation was not necessary. In those 17, the mean duration of noninvasive positive-pressure ventilation was 6.3 days. We conclude that noninvasive positive-pressure ventilation can improve gas exchange in patients with acute hypercapnea complicating chronic respiratory failure.