An exercise test was devised to investigate the relationship between power and endurance for treadmill running. The subjects were 19 males aged 21-25 yr (11 distance runners and 4 sprinters of provincial grade, and 4 non-competitive runners). Each subject ran to exhaustion on a treadmill at 15 km hr-1 at five different inclinations (31%-9%), giving maximum performance times in the range 10 s to 3 min. An iterative least-squares procedure was used to fit the following exponential model to each subject's data: It = I infinity + (I0-I infinity) exp (-t/tau), where It, I0 and I infinity are inclinations at time t = t, t = 0 and t----infinity, and tau is a time constant. The fit was excellent (r2 = 0.96-1.00). I0 and I infinity are interpreted as measures of maximum anaerobic (instantaneous) and maximum aerobic (continuous) power respectively. Inclinations corresponding to performance times of 10-180 s (I10-I180) were calculated from these parameters. Test-retest reliability was highest for I0-I30 (intraclass r = 0.97-0.94), lower for I60-I infinity (r = 0.89-0.84), and lowest for tau (r = 0.78). Good correlations were observed between I0-I30 and peak power in a 30 s all-out test on a cycle ergometer (r = 0.73-0.81), and between I180, I infinity and maximum oxygen consumption (r = 0.87, 0.81). The test may be useful for ranking or monitoring running performance for events of up to 1 min duration.