The StairMaster 4000 PT is a popular step ergometer which provides a submaximal test protocol (SM Predicted V̇O2max) for the prediction of V̇O2max (ml·kg-1·min -1). The purpose of this study was to evaluate the SM Predicted V̇O2max protocol by comparing it to results from a V̇O 2max treadmill test in 20 young healthy women aged 20-25 years. Subjects were 10 step-trained (ST) women who had performed aerobic activities and exercised on a step ergometer for 20-30 minutes at least 3 times per week for the past 3 months, and 10 non-step-trained (NST) women who had performed aerobic activities no more than twice a week during the past 3 months and had no previous experience on a step ergometer. The SM Predicted V̇O 2max protocol used 2 steady state heart rates between approximately 115-150 b·min-1 to estimate V̇O2max. The Bruce maximal treadmill protocol (Actual V̇O2max) was used to measure V̇O2max by open circuit spirometry. Each subject performed both tests within a 7-day period. The means and standard deviations for the Actual V̇O2max tests were 39.8 ± 6.1 ml·kg -1·min-1 for the ST group, 37.6 ± 6.3 ml·kg-1·min-1 for the NST group, and 38.7 ± 6.2 ml·kg-1·min-1 for the Total group (N = 20); and for the SM Predicted V̇O2max tests, means and standard deviations were 40.78 ± 14.0 ml·kg -1·min-1, 30.9 ± 4.8 ml·kg -1·min-1 and 35.9 ± 11.4 ml·kg -1·min-1. There was no significant difference (p > 0.05) between the means of the Actual V̇O2max and SM Predicted V̇O2max test for the Total group (N = 20) or the ST group (n = 10), but a significant difference (p < 0.05) was shown for the NST group. The coefficient of determination (R2) and standard error of estimate (SEE) for the SM Predicted V̇O2max and Actual V̇O2max tests were R2 = 0.18, SEE = 5.72 ml·kg-1·min-1 for the Total group; R 2 = 0.00, SEE = 6.68 ml·kg-1·min -1 for the NST group; and R2 = 0.33, SEE = 5.32 ml·kg-1·min-1 for ST group. In conclusion, the SM Predicted V̇O2max test has acceptable accuracy for the ST group, but significantly underpredicted the NST group by almost 7 ml; and, as demonstrated by the high SEEs, it has a low level of precision for both ST and NST subjects.