The purpose of this investigation was to identify a perceptually based warning zone to anticipate termination of Bruce treadmill tests. Apparently healthy adult women (n = 116) and men (n = 55) participated. The time to test termination was measured from the point during the treadmill test at which participants estimated a rating of perceived exertion of 12, 13, 14, 15, 16, and 17 using the Borg 6-20 scale to specify the rating of perceived exertion which was less than or equal to one exercise test stage. Women exercised for 141.9 +/- 99.2 sec. after reporting a rating of perceived exertion of 14. Men terminated the treadmill test 120.1 +/- 80.0 sec. after estimating their rating of perceived exertion to be 15, indicating volitional test termination will occur before the next exercise stage is completed. Accurate and timely prediction of test termination using ratings of perceived exertion may enhance the safety of exercise tests administered to apparently healthy adults and facilitate obtaining endpoint measures upon which to prescribe exercise intensity.