A multidisciplinary pulmonary rehabilitation program was conducted for 13 outpatients (mean age 66 +/- 6.7 yr) with moderately severe chronic obstructive pulmonary disease. Changes in pulmonary function and blood gas data were not significant. Exercise capability, including 6-minute walking distance (WkD6), maximal work load (WkLmax), endurance time, and maximum heart rate, improved significantly (p < 0.05), as did subjective symptoms and quality of life. Of the observed changes, only baseline PaO2 and oxygen saturation were positively correlated with changes in maximum heart rate. The initial maximum heart rate was inversely related to both the absolute and percentage improvement. There were no significant relationships between improvement in WkD6 and age, initial arterial blood gas, or pulmonary function, but a significant relationship was found between baseline forced expired volume in the first second (FEV1) and percentage change in WkLmax. Our results indicate that patients with moderately severe chronic obstructive pulmonary disease can improve their exercise capacity, subjective symptoms, and quality of life through a pulmonary rehabilitation program. All patients can increase their endurance, regardless of their initial exercise performance. Maximum heart rate and FEV1 are predictors of exercise capability improvement.