A new classification for the severity of COPD was proposed at GOLD 2003: stage I: FEV(1) > or = 80% predicted; stage II: 50% < or = FEV(1)<80%; stage III: 30% < or = FEV(1)<50%; and stage IV: FEV(1) < 30%. To elucidate the acute effects of pulmonary rehabilitation (PR) on patients with different stages of COPD, data on pulmonary function, arterial blood gas analysis, the 6-min walk test, respiratory muscle strength, and activities of daily living were analyzed before and after our comprehensive 4- to 8-week inpatient PR program between 1992 and 2003. A total of 225 patients (201 men and 24 women; 21 with stage II, 79 with stage III, and 125 with stage IV COPD) was assessed. There were significant differences in FEV(1)% predicted and % residual volume in stages III and IV, in % vital capacity in stages II, III and IV, and in % total lung capacity in stage II when comparing the changes between pre- and post-PR. Significant differences of PaO(2) in stages III and IV and PaCO(2) in stage IV were found when comparing the changes between pre- and post-PR. The 6-min walk distance was significantly increased after PR by an average of approximately 50m for all staged patients. Respiratory muscle strength was also significantly increased in stages III and IV. Activities of daily living were significantly improved in all stages. These results showed that patients with COPD had benefited from PR regardless of disease severity. The effects included improvement in pulmonary function, arterial blood gas analysis, 6-min walk distance, respiratory muscle strength, and activities of daily living although there were some differences among the three stages.