Laboratory and field assessments were made on eighteen male distance runners. Performance data were obtained for distances of 3.2, 9.7, 15, 19.3 km (n = 18) and the marathon (n = 13). Muscle fiber composition expressed as percent of slow twitch fibers (%ST), maximal oxygen consumption (Vo2max), running economy (Vo2 for a treadmill velocity of 268 m/min), and the Vo2 and treadmill velocity corresponding to the onset of plasma lactate accumulation (OPLA) were determined for each subject. %ST (R greater than or equal to .47), Vo2max (r greater than or equal to .83), running economy (r greater than or equal to .49), Vo2 in ml/kg min corresponding to the OPLA (r greater than or equal to .91) and the treadmill velocity corresponding to the OPLA (r greater than or equal to .91) were significantly (p less than .05) related to performance at all distances. Multiple regression analysis howed that the treadmill velocity corresponding to the OPLA was most closely related to performance and the addition of other factors did not significantly raise the multiple R values suggesting that these other variables may interact with the purpose of keeping plasma lactates low during distance races. The slowest and fastest marathoners ran their marathons 7 and 3 m/min faster than their treadmill velocities corresponding to their OPLA which indicates that this relationship is independent of the competitive level of the runner. Runners appear to set a race pace which allows the utilization of the largest possible Vo2 which just avoids the exponential rise in plasma lactate.