We evaluated the conditions of 33 patients who completed an outpatient pulmonary rehabilitation program to determine what types of improvements occurred, and whether these changes were related to the baseline degree of ventilatory impairment, to determine whether rehabilitation was beneficial to patients, regardless of the degree of underlying lung dysfunction. Endurance measurements, including sustained submaximal performance on a cycle ergometer and the 12-minute walk distance (1,349 +/- 625 feet to 1,700 +/- 670 feet) increased significantly (p less than 0.01), as did multiple educational and subjective parameters. Maximal exercise performance on a graded cycle test improved very little, with a decline in the ventilatory equivalent for oxygen consumption (VE/VO2) being the only significant change (48.2 +/- 28.3 L/ml to 36.6 +/- 8.7 L/ml). Of the observed changes, only one endurance measurement, the sustained submaximal exercise performance, correlated with FEV1 (r = 0.5, p less than 0.01), but only if it was expressed as an absolute number (liters) and not as percent predicted. Lung function did not correlate with changes in the 12-minute walk distance, in maximal exercise performance on the cycle ergometer or with changes in educational and subjective parameters. We conclude that because the magnitude of change in both physiologic and psychologic parameters was not directly related to lung function, the benefits of rehabilitation can extend to all patients with chronic lung disease, regardless of the severity of preexisting pulmonary dysfunction.