Heat-acclimated men (n = 10) and women (n = 9) were exposed to hot-dry conditions (49 degrees C, 20% rh) for 4h to determine the effect of prolonged work in the heat on physiological differences between the sexes. Hourly exposures consisted of 10 min resting and 50 min walking at 1.34 m . s-1 (time-weighted metabolic rate = 175 and 151 W . m-2 for men and women, respectively). No significant difference in rectal temperature (Tre) was found between the sexes for each hour (h) of exposure. Heart rate (HR) of women, however, averaged 10-17 beats . min-1 higher than men. Mean skin temperature (Tsk) was also significantly higher in women throughout the exposure. For both sexes, the 4th-h Tre, HR, and Tsk were significantly higher than the preceding 3h. No sex related differences in total sweat rate (msw) or sweat sensitivity, as indicated by msw/delta Tre, were evident. It was concluded that: a) prolonged exposure to dry heat does not accentuate physiological differences between the sexes; b) women sweat at rates comparable to men over a 4-h period; c) 2-h acclimation sessions do not necessarily acclimate individuals for work of longer duration.