OBJECTIVE: To determine if there is a dosage effect associated with the length of pulmonary rehabilitation (PR). METHOD: We used a battery of outcome measures to quantify the amount of change that was achieved from baseline to discharge in 286 patients completing a PR program in 1 of 12 institutions participating in PROAS. The programs were of varying durations. Paired t-tests indi-cated overall that while the pulmonary rehabilitation programs did not yield improvements in physio-logic (FEV1,FVC,% predicted FEV1) outcomes, the patients did achieve signifi-cant improvements in symptomatic (Borg score), functional (6-minute walk), general health-related quality of life [SF-36 Health Survey (SF-36)], and disease-specific HRQL [Chronic Respiratory Disease Questionnaire (CRQ)] variables. RESULTS: Based on a series of stepwise multiple regressions using the amount of change in each outcome variable as the dependent variable and adjusting for the corresponding baseline value and 11 clinical and sociodemographic characteristics, the number of hours of education (HREDU, 13.5hr±6.7), activi-ties of daily living (HRADL, 2.2hr±6.6), and psychosocial support (6.5hr±5.6) both individually and collectively (42.4hr±11.8) generally did not contribute to explaining the magnitude of change achieved by the patients. However, the number of hours of su-pervised exercise (HREX, 25.4hr±9.2) did contribute to explaining increases in 5 of the 8 SF-36 domains: physical function (p=0.027), physical role (p=0.0002), health perceptions (p=0.0167), vitality (p=0.034) and social function (p=0.0035). CONCLUSION: These data suggest that outcomes specifically related to pulmonary diseases are not affected by a longer duration for this type of intervention, but that broader, population-based assessments may need an additional period of intervention, or elapsed time, to detect improvement.