This study compared the effects of a high-carbohydrate and a mixed diet on core temperature responses to prolonged exercise in six male competitive cyclists (age = 22.2 +/- 1.9 years). This study, the first to investigate the effect of a high-carbohydrate diet on exercise core temperature in humans, therefore suggests that three days of increased dietary carbohydrate intakes do not evoke any deleterious thermoregulatory responses during prolonged submaximal exercise.