Significant qualitative and quantitative data from the literature suggests that men and women differ in their response to extreme thermal environments. It is apparent that women sweat less (Morimoto et al., 1967; Wyndham et al., 1965), and have a thicker subcutaneous fat layer (Wells, 1991) relative to men. Men, on the other hand have higher resting and working metabolic rates relative to women, which tend to increase their core body temperatures at a faster rate. A whole body thermal regulation model (Wissler, 1985) designed by Gene Wissler is used to analyze the gender based thermal responses of men and women subjected to medium-high work levels in several thermal environments. This study has important application in estimating how gender differences affect the potential work performance of men and women in extreme thermal environments.