The purpose of this study was twofold: (a) determine metabolic cost of StairMaster (STM) exercise, and (b) compare heart rate (HR) and rating of perceived exertion (RPE) during treadmill (TM) and STM exercise at similar metabolic work rates. Respiratory gases, HR, and RPE were measured while walking and running on the TM and exercising on the STM. Ten fit males and females were subjects. Peak VO2 on the TM was 50.9 ml O2 kg-1 min-1 while peak attainable VO2 on the STM was 41.5 ml O2 kg-1 min-1. No difference was seen between the TM and STM HR or RPE when steady-state workloads of equivalent oxygen uptakes were observed. Actual oxygen uptake during the 6 MET, 8 MET, and 10 MET STM stages averaged 4.5 ml O2 kg-1 min-1 lower than predicted VO2 for these work intensities. The results of this study indicate that metabolic rate is overestimated by the StairMaster computer program and that peak VO2 on the StairMaster is approximately 41 ml O2 kg−1 min−1. Although that intensity is not sufficient to reach the maximum oxygen uptake of fit young athletes, it is sufficiently intense to reach at least 50% of maximum VO2 of even the most aerobically fit athlete. The heart rate/VO2 relationship found in this study indicates that the existing target heart rate equations for determining exercise intensity are suitable for use on the StairMaster. © 1993 National Strength and Conditioning Association.