The purposes of this study were to test the validity of a recent scale based on the estimation of a time of exhaustion (entitled Estimated Time Limit scale) to predict a time limit (Tlim) and to regulate exercise intensity and to investigate the reliability of the Estimated Time Limit scale and the Ratings of Perceived Exertion (RPE) scale. 14 male runners performed one incremental test, one constant velocity test at 85% of Maximal Aerobic Velocity (MAV), one constant duration test and one retest of 15 min. on an outdoor track. The difference between Estimated Time Limit values obtained during the incremental test at 85% MAV and measured Tlim values during the constant velocity test were examined, the velocities at ETL=13 (i.e., 15 min.) obtained during the incremental test were compared with measured velocities during the constant duration test or the retest (only the best performance was used), and RPE and Estimated Time Limit values during the constant duration test were compared with those measured during retest. The results have shown a nonsignificant correlation between Estimated Time Limit values at 85% MAV and measured Tlim values during constant velocity test. There was a significant correlation (p<.02, r = .64) between velocities at ETL=13 and measured velocities. However, the slope and y intercept value of this regression were significantly different from those of the identity line. There was no significant difference between constant duration test and retest for the values of RPE and Estimated Time Limit with high correlations (between r = .77 and .99 for RPE scale, and r = .74 and .99 for Estimated Time Limit scale). Moreover, the regression lines were close to the identity line. The RPE and Estimated Time Limit scales are reliable, but the lack of validity for the Estimated Time Limit scale suggests that more studies must be performed before using this scale to predict Tlim and regulate exercise intensity in male runners.