The present study examined the impact of the menstrual cycle and oral contraceptive use on performance of high-intensity intermittent running in the heat [31.0 (0.2) degrees C; 23.1 (0.9)% relative humidity]. Seven normally menstruating women (NM) and eight oral contraceptive (OC) users participated in the study. Two trials were undertaken near the predicted mid-point of the follicular (FT) and luteal (LT) phases of the menstrual cycle and the equivalent days for the OC users. Basal serum progesterone concentrations were higher during the LT for the NM group [FT: 2.42 (0.28) nmol l(-1) vs LT: 25.96 (11.28) nmol l(-1); P<0.05], but were not different for the OC users [days 1-14: 2.79 (0.38) nmol l(-1) vs days 15-28: 2.61 (0.32) nmol l(-1)]. There were no differences in distance run between menstrual cycle phases or between the normally menstruating and OC groups [NM FT: 6257 (1401) m vs LT: 5861 (1035) m]. However, the OC ran further in days 15-28 compared to days 1-14 [OC 1-14: 5481 (612) m vs 15-28: 6615 (893) m, P<0.05]. For the NM, rectal temperature, perceived exertion, estimated SR, serum growth hormone, plasma lactate, ammonia and glucose did not differ between phases of the menstrual cycle. For the OC group, heart rate, perceived exertion, sweat rate, plasma lactate and ammonia did not differ between days 1-14 of OC use and days 15-28. However, rectal temperature was higher ( P<0.05) and growth hormone tended to be higher ( P=0.05) during days 15-28, while plasma glucose was lower ( P<0.05). These results demonstrate that for unacclimatised games players the performance of intermittent, high-intensity shuttle running in the heat is unaffected by menstrual cycle phase but is influenced by OC use.