The effect of a 6 wk period of ventilatory muscle endurance training on the maximal sustained ventilatory capacity (MSVC) and on exercise tolerance was examined in 10 patients with chronic obstructive pulmonary disease (COPD). No significant changes occurred in lung volumes or spirometric indices. After training the MSVC increased from 32 .+-. 11 to 42 .+-. 131/min (P < 0.001) and the MSVC/FEV1 [forced expiratory volume in 1 s] ratio from 40.2 .+-. 8.8 to 47.8 .+-. 8.0 (P < 0.001). O2 consumption during the MSVC increased from 460 .+-. 94 to 647 .+-. 107 ml/min (P < 0.001), and MSVC heart rate increased from 99 .+-. 15 to 114 .+-. 15 (P < 0.001). The post MSVC blood lactate increased from 1.55 .+-. 1.29 to 2.85 .+-. 1.05 mM (P < 0.001). Maximal exercise ventilation measured by an incremental ergometer test increased from 32 .+-. 8 to 36 .+-. 11.5 l/min for leg exercise and from 30.4 .+-. 8.4 to 33.7 .+-. 8.9 l/min (P < 0.01) for arm exercise. Endurance time at a constant submaximal load increased from 6.98 .+-. 4.30 to 10.76 .+-. 6.00/min (P < 0.01) for leg exercise and from 5.76 .+-. 3.53 to 10.47 .+-. 6.57/min (P < 0.01) for arm exercise. The maximal distance covered in a 12 min walk increased from 1058 .+-. 161 to 1188 .+-. 201 m (P < 0.01). Ventilatory muscle training in COPD patients improved the ventilatory muscle performance, as indicated by the increased MSVC, O2 consumption during the MSVC and the maximal exercise ventilation. There was a substantial increase in submaximal exercise endurance for both arm and leg work.