We studied high intensity, symptom-limited, endurance exercise training in 52 patients with COPD participating in a pulmonary rehabilitation program. The patients had moderate to severe airway obstruction and reduced exercise tolerance with ventilatory limitation. The target workload for endurance exercise testing was 95 percent of the baseline maximum treadmill work load. At training weeks 1, 4 and 8, they were training at 85, 84, and 86 percent respectively, of baseline maximum. After rehabilitation, there was an increase in maximal treadmill work load, VO2max, and endurance exercise time, and a decrease in perceived symptoms. Patients who did not reach anaerobic threshold (group 2) were able to train at a higher percentage of maximum exercise tolerance than patients who reached anaerobic threshold (group 1). The increase in exercise performance of both groups, however, was similar. We conclude that patients with moderate to severe COPD can perform exercise training successfully at intensity targets which represent higher percentages of maximum than typically recommended in normal individuals or other patients.