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Thirty-eight young adult males were exercised daily for 2 weeks on a motor-driven treadmill at 3.5 mph located in a heat chamber maintained at 98F. dry bulb and 90F. wet bulb. Twelve subjects walked for 50 minutes followed by 10 minutes rest in the heat; 13 subjects walked 50 minutes, rested 10 minutes, walked 30 more minutes and rested a final 10 minutes; 13 subjects walked 50 minutes, rested 10 minutes, walked 50 more minutes and rested a final 10 minutes. A modified Balke performance test was administered before heat exposure and at the end of each week. Physiological parameters including rectal temperatures, heart rates, sweat loss and sweat electrolytes were used as measures of acclimatization. It was found that the daily exposure to heat for 1 hour did not produce acclimatization as seen in the latter groups. Several differences between physiologic adjustment to a hot-wet as contrasted with hot-dry climates were observed and are discussed. (Author)