The purpose of this study was to examine the testosterone, cortisol, and the molar ratio of testosterone to cortisol (T:C) blood concentration responses to intermittent, high intensity exercise in the heat. Eight active men [mean age 25 (SD 3) years, mass 71.1 (SD 5.5) kg, height 175.9 (SD 4.4) cm] performed two series of five 15-s Wingate anaerobic power tests in both hot (H, 35 degrees C) and thermoneutral (TN, 22 degrees C) environments. Each period of exercise was separated by 30-s of active recovery. Each series was separated by 60 min of passive recovery. Blood samples were obtained before (PRE), immediately post (IP), and 5(5R), 10(10R), 15(15R), 30(30R), 45(45R), and 60(60R) min following exercise. Peak power was significantly higher, during the first series of exercise, in the H compared to TN. No significant differences were seen in any of the variables between the first and second series of exercise in either environmental condition. Furthermore, no significant differences between these conditions were observed in heart rate, blood lactic acid concentration, or rectal temperature. A significant decrease in cortisol concentration was observed between PRE and IP, during both conditions. However, no significant interactions between TN or H were seen. No change from PRE was observed in testosterone or T:C during either TN or H. It would appear that testosterone and cortisol respond similarly to repeated periods of short duration high intensity exercise, in either thermoneutral or moderately hot environments.