The 6-minute walk test (6MWT) is used to predict aerobic capacity, evaluate functional performance, and assess the risk of mortality and morbidity of several chronic conditions. The purpose of this study was to determine the validity and reliability of the 6MWT on a treadmill, thus increasing the clinical use of the 6MWT. Participants comprised 20 able-bodied persons (9 men, 11 women, 29.5 +/- 9.7 years, 1.73 +/- 1.0 m, 72.76 +/- 18.92 kg). All participants reported being nonsmokers and without any known cardiopulmonary, neurological, or orthopedic conditions. Participants took part in 3 repeated treadmill 6MWTs (T6MWTs) and a graded cycle ergometer test to determine maximum oxygen consumption (VO2max). No statistically significant differences were found between the 3 T6MWTs for distance, rating of perceived exertion, or heart rate (HR) (P = .17, .47, and .44, respectively) using both a repeated measures 1-way analysis of variance and an intraclass correlation coefficient (model 2, 1). The reliability was best between the second and third T6MWTs for distance and HR (0.88 and 0.86, respectively). A predictive equation from the stepwise linear multiple regression was used: VO2max (L/min) = -1.732 + (weight [kg] x 0.049) + (distance [m] x 0.005) + (HR [beats/min] x [-0.015]), r = 0.869, SEE = 0.399. The Bland-Altman plot found 95% of the data points within the limits of agreement. The T6MWT protocol was found to be reliable for measuring distance and HR. It can reasonably predict absolute VO2max in a healthy adult population and should be validated in those with established chronic disease.