Previous studies have reported strong correlations between 5-km performance times and maximal oxygen uptake (VO2 max) and also for running speeds equivalent to blood lactate concentrations of 4 mM. However, there is little information on the physiological responses of individuals during races over this distance. Therefore, the aim of the present study was to measure the physiological and metabolic responses of endurance trained male (n = 8) and female (n = 8) runners during a 5-km time trial using an instrumented treadmill. Performance times were 18.77 +/- 1.27 min for the men and 21.80 +/- 1.98 min for the women (P less than 0.01). The corresponding times on the athletics track were 17.68 +/- 0.39 min for the men (P less than 0.05) and 20.70 +/- 2.16 min for the women (N.S.). During the treadmill time trials, both the men and women were able to utilize approximately 90% VO2 max, 82% VE max, 98% HR max and produce similar concentrations of blood lactate. Although the physiological and metabolic responses of these endurance-trained men and women to 5-km treadmill running were similar, the faster running times recorded by the men in this study were the result of their higher VO2 max values.