Background: Submaximal exercise tests use heart rate responses to low-to-moderate intensity activity in order to predict cardiorespiratory fitness (VO2max). Currently used tests may be inappropriate for obese populations as obese women have altered heart rate responses to exercise. The purpose of this study is to test the validity of the Modified Bruce Protocol submaximal treadmill test in obese women. Methods: Normal-weight (NW) women and obese (OB) women completed the Modified Bruce submaximal treadmill test (to predict VO2max using previously validated equations) and a maximal graded exercise test on a treadmill using the Standard Bruce Protocol (to obtain an actual VO2max) on two separate occasions. The relationships between actual and predicted VO2max values were analyzed using correlation coefficients. Results: 9 NW (age: 23.1 ± 8.0 y, body fat: 23.5 ± 4.9%) and 9 OB (age: 22.0 ± 4.8 y, body fat: 36.9 ± 4.4%) women participated. Actual and predicted VO2max values were not correlated among the OB women (r = 0.48, P = .23) but were positively correlated among the NW women (r = 0.71, P = .03). When actual VO2max was expressed per kilogram lean body mass, the relationships between actual and predicted VO2max remained (OB: r = .20, P = .60; NW: r = .80, P = .009). Conclusions: Protocols for predicting fitness in NW women do not appear to be valid in OB women. Separate equations should be considered in order to maximize the accuracy of exercise testing in OB women, and thus improve health care providers’ ability to evaluate patients and tailor exercise prescriptions.