We examined the effect of a 6-wk period of ventilatory muscle endurance training on the maximal sustained ventilatory capacity (MSVC) and on exercise tolerance 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 +/- 13 l/min (P less than 0.001) and the MSVC/FEV1 ratio from 40.2 +/- 8.8 to 47.8 +/- 8.0 (P less than 0.001). Oxygen consumption during the MSVC increased from 460 +/- 94 to 647 +/- 107 ml/min (P less than 0.001), and MSVC heart rate increased from 99 +/- 15 to 114 +/- 15 (P less than 0.001). The post MSVC blood lactate increased from 1.55 +/- 1.29 to 2.85 +/- 1.05 mM/l (P less than 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 less than 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 less than 0.01) for leg exercise and from 5.76 +/- 3.53 to 10.47 +/- 6.57/min (P less than 0.01) for arm exercise. The maximal distance covered in a 12-min walk increased from 1,058 +/- 161 to 1,188 +/- 201 m (P less than 0.01). We concluded that ventilatory muscle training in patients with COPD improved the ventilatory muscle performance, as indicated by the increased MSVC, oxygen consumption during the MSVC, and the maximal exercise ventilation. There was a substantial increase in submaximal exercise endurance for both arm and leg work.