With the aim of testing a method that allows increasing concentrations of oxygen to be administered to patients with severe hypoxemia and hypercapnia while avoiding the risk of increasing respiratory acidosis, we studied 17 male patients with advanced chronic obstructive pulmonary disease (COPD) and severe hypercapnic respiratory failure. During 6 h and on one day only, all patients were given intermittent negative pressure ventilation (INPV) together with oxygenation starting at a concentration of 24 percent and increasing to 30 percent. Using this procedure, it was possible to raise arterial PaO2 to safe levels (from 47.2 +/- 3 mm Hg to 61.5 +/- 6 mm Hg, p less than 0.001) without increasing hypercapnia, and a significant drop in PaCO2 levels (from 74.4 +/- 9 mm Hg to 65.6 +/- 12 mm Hg, p less than 0.005) was even observed. One hour after INPV ended, the mean values of PaO2, PaCO2, oxygen saturation, and pH were also significantly better than prestudy values. We conclude that INPV and oxygen therapy with increasing oxygen flow could constitute an alternative option to intubation and mechanical ventilation in cases of severe hypercapnic respiratory failure due to advanced COPD.