The 6-min walk test (SMWT) performed in the hallway (HW) is used as a clinical indicator of functional capacity in patients with lung disease. A 6-min walk test utilizing a treadmill (TM) is easier to perform and allows easier patient monitoring. Therefore, we formulated a standardized TM SMWT protocol and compared the results with those of a HW SMWT. All patients were enrolled in a pulmonary rehabilitation program. Patients with current infection, recent change in inhaled medications or oral steroid use, and significant cardiovascular disease were excluded. Each subject performed three HW SMWTs and three TM SMWTs assigned randomly on subsequent days. There was a 30-min rest between each walk and at least a 48-h rest between each test day. All patients completed both HW and TM SMWT within 7 d. Supplemental oxygen was utilized or increased if the saturation fell below 88%. The best of the three tests was used for data analysis. Twenty-one subjects completed the protocol. The mean age was 65 +/- 10.9 yr (range, 35 to 79 yr). Ten subjects were receiving supplemental oxygen. The mean FEV(1) was 1.07 +/- 0.53 L. The mean HW SMWT distance was 1,228 +/- 255 ft (range, 612 to 1,679 ft) and the mean TM SMWT distance was 1,060 +/- 389 ft (range, 475 to 1,819 ft), which were statistically different (p = 0.01). The mean difference was 168 +/- 280 ft (range, -326 to 743 ft). Oxygen saturation and supplemental oxygen requirements did not differ significantly. The intra-test variability of the three HW SMWTs was similar to the three TM SMWTs and no significant difference in the coefficient of variation was found. A standardized TM SMWT is feasible and allows easier patient monitoring, but there is a statistically significant difference between the HW and TM SMWT distance and therefore they are not interchangeable. However, the intratest reproducibility of the TM and HW SMWTs are similar when three walks are performed in a single test session. The role of the TM SMWT in pulmonary rehabilitation requires further exploration.