We evaluated retrospectively the effect of long-term oxygen therapy (LTOT) on the prognosis of 35 patients with chronic obstructive pulmonary disease (COPD) and chronic respiratory insufficiency (group A) who were admitted to our respiratory intensive care unit from 1984 to 1986 for acute respiratory failure (ARF). All subjects were given intermittent negative pressure ventilation (INPV) by means of an iron lung to overcome the acute episode and were treated with LTOT after discharge. Forty-four patients with COPD who were treated with the same ventilatory method to overcome an acute disease exacerbation and who were not given LTOT were used as controls (group B). Both groups were followed up for at least 48 months. All relapses of ARF were treated by iron lung in both groups A and B. The overall survival was significantly better in group A than in group B (p = 0.05 by F test) indicating that LTOT improves survival in patients with COPD after a bout of ARF treated with mechanical ventilation. Therefore, combining INPV with LTOT for overcoming acute episodes and relapses of ARF appears to improve the prognosis of patients with COPD.