The purpose of this study was to determine the effect of pre-exercise cooling on high intensity, moderate duration running performance and thermoregulatory responses in a hot environment (38 degrees C, 40 %RH). On separate days, 11 male subjects completed two treadmill runs to exhaustion at 100% of maximal aerobic power with (CL) and without (CT) pre-exercise cooling. Cooling consisted of 20 min of standing rest in a 22 degrees C environment with fan cooling (4.0 m x sec -1) and water spraying (50 ml x min -1) applied to both anterior and posterior body surfaces. Core temperature (T(c)) was determined with an esophageal T(es) probe, and skin temperatures (T(sk)) were measured using surface thermistors positioned at four sites. Finger prick blood samples were taken before and after exercise for the determination of blood lactate. Heart rates and ratings of thermal sensations and comfort were also recorded. Time to exhaustion was significantly shorter in the CL condition (368.9 +/- 56.2) compared to the CT condition (398.8 +/- 55.5 sec). Peak T(es) (37.51 +/- 0.57 vs. 38.56 +/- 0.30 degrees C for CL and CT, respectively), T(sk) (34.18 +/- 1.22 vs. 36.15 +/- 0.70 degrees C for CL and CT, respectively), rates of heat gain (0.20 +/- 0.05 vs. 0.28 +/- 0.05 degrees C x min -1 for CL and CT, respectively), and net heat storage (238.4 +/- 109.6 vs. 531.9 +/- 78.3 kJ for CL and CT, respectively) were all lower in the CL compared to CT throughout the treadmill runs. There were no differences in lactate accumulation between the two conditions. Based on these data, it can be concluded that pre-exercise cooling influences thermoregulatory responses during high intensity, moderate duration exercise; however, performance is impaired compared to a control trial in which no cooling procedures were employed.