OBJECTIVES--To assess the efficacy of a 9-minute walking test on a self-powered treadmill in a group of patients with various degrees of heart failure, to investigate the reproducibility of the technique, and to establish the safety of the technique. PATIENTS AND METHODS--24 controls and 37 patients with various grades of heart failure were studied. Peak oxygen consumption was measured in patients and controls. The distance walked in 9 minutes on a self-powered treadmill was measured in all groups and the test was repeated to assess reproducibility. RESULTS--The distance walked in 9 minutes correlated with peak oxygen consumption in patients, controls, and both groups combined. There was a significant difference in the distance walked by controls and patients and in the distance walked by patients with severe rather than with mild or moderate heart failure. There was no significant difference between the results of successive 9-minute walking tests in any group. No serious adverse reaction was seen in any patient during or after the test. CONCLUSION--The 9-minute walking test on a self-powered treadmill is a sensitive, reproducible, safe, and inexpensive method of assessing functional capacity in patients with all grades of heart failure.