The addition of noninvasive positive pressure ventilation (NPPV) to an exercise training (ET) program in severe chronic obstructive pulmonary disease (COPD) may produce greater benefits in exercise tolerance and quality of life than after training alone. Forty-five patients with severe stable COPD-mean (SD) FEV(1) 0.96 (0.31) L, Pa(O(2)) 65.4 (9.07) mm Hg, Pa(CO(2)) 45.6 (7.89) mm Hg-were randomized to domiciliary NPPV + ET (n = 23) or ET alone (n = 22). Exercise capacity and health status were assessed at baseline and after an 8-wk training program. There was a significant improvement in mean shuttle walk test (SWT) in the NPPV + ET group: from 169 (112) to 269 (124) m (p = 0.001), compared with the ET group: 205 (100) to 233 (123) m (p = 0.19); mean difference (95% confidence interval [CI]): 72 (12.9 to 131) m. Repeated measures analysis of variance (ANOVA) showed that the differences between the two groups became evident only in the final 4 wk of the training program with a mean end study difference (95% 1CI) of 65.8 (17.1 to 114) m. There was a significant improvement in the Chronic Respiratory Disease Questionnaire (CRDQ) of mean (SD) 24.0 (17.4) (p = < 0.001) in the NPPV + ET group and 11.8 (15.8) (p = 0.003) points in the ET group; mean difference: 12.3 (1.19 to 23.4). Only the NPPV + ET group demonstrated a significant improvement in arterial oxygenation; mean difference: 3.70 mm Hg (0.37 to 7.27). This study suggests that domiciliary NPPV can be used successfully to augment the effects of rehabilitation in severe COPD.