Little if any research has examined the variability in time to exhaustion (TTE) during submaximal treadmill running. This study investigated the test-retest reliability of submaximal treadmill TTE as a measure of endurance capacity. Sixteen endurance-trained males (n=14) and females (n=2) completed a run to exhaustion at 70% (T1) and repeated the same run three weeks later (T2). At 30 min intervals during each run, expired gas, heart rate (HR) and ratings of perceived exertion (RPE) were collected. Mean ± SD TTE was 96 ± 20 min in T1 versus 101 ± 29 min in T2 (P=0.3). The mean ± 95% confidence intervals (CI) of the coefficient of variance (CV) was 5.4% (1.4 – 9.6). The average intraclass correlation coefficient (±95% CI) was 0.88 (0.67 – 0.96) between trials. The respiratory-exchange ratio was not different between trials, T1: 0.87±0.1 and T2: 0.89±0.1 (P>0.05) and neither was total whole-body carbohydrate oxidation (2.1±0.4 g·min-1 and 2.3±0.6 g·min-1), fat oxidation (0.6±0.2 g·min-1), HR (178±8 and 175±7 beats·min-1) or RPE (17±3 and 16±3). These results suggest that use of prolonged treadmill-based TTE can be a reliable research tool to assess human endurance capacity in aerobically-trained men and women.