Oxygen supplementation is known to improve exercise capacity in patients with chronic obstructive pulmonary disease (COPD). Although some COPD patients use oxygen after exercise to relieve dyspnea, the effect of oxygen during recovery from exercise is not clearly understood. Exercise duration and dyspnea recovery time were studied in 18 patients with stable COPD. Patients exercised at a constant submaximal work rate on a treadmill ergometer until they no longer wished to continue. Oxygen, room air and compressed air were randomly administered in three consecutive post-exercise recovery periods. Dyspnea was scored on a 100 mm visual analog scale at 30 s intervals until return to baseline. An additional 20 minute post-recovery resting period was allowed between each test. No significant differences were found in dyspnea recovery time breathing oxygen (271 s), room air (290 s) or compressed air (311 s) When the groups were sorted by sequence of testing, there was a highly significant increase in recovery time (208 s, 307 s and 358 s for the first, second and third tests; P < 0.005) and a non-statistically significant decrease in exercise duration (89 s, 79 s and 76 s). Post-exercise oxygen supplementation had no effect on dyspnea recovery time in these COPD patients. Repeated bouts of exercise increased dyspnea recovery time and tended to decrease exercise duration. These findings suggest that, despite recovery of symptoms, physiological recovery from prior exercise is incomplete.