In brief: Recent studies suggest that there are few differences in men's and women's responses to heat stress when they are matched for Vo2max. Although early studies reported that women are less tolerant of exercise in the heat than men, this may have been because the women had lower fitness levels. In hot, humid environments women have an advantage in losing heat because of their larger surface-area-to-weight ratio, even though men lose more sweat. Training lowers women's threshold for sweating and improves their tolerance for exercise in the heat. During road races the frequency of heat illness is approximately the same for men and women.