The effects of several uniform configurations on fluid and electrolyte losses in a hot environment (30 degrees C db, 18 degrees C wb) were studied in 15 healthy males, during 6 h of intermittent treadmill exercise (1.56 m.s-1, 0% grade, 50 min.h-1, 28 km total distance). The uniforms were: the temperate battle dress uniform (BDU), two variants (C and F) of full military oriented protective posture (MOPP IV), and MOPP IV with no mask or hood (M). Sweat rate, urine volume, electrolyte losses (Na+, Cl-, K+, Mg++, Ca++) in sweat and urine, rectal temperature, mean skin temperature, heart rate, and temperature/humidity inside uniforms were measured. Observations indicated that both MOPP IV configurations (C and F) resulted in significantly greater (p. less than 0.05) fluid losses and physiological strain than BDU and M. However, there were no between-uniform differences in the total loss of any electrolyte. Total body fluid losses (kg.6h-1) and electrolyte losses in sweat (mEq.6h-1) were consistently greater than in urine. It was concluded that 6 h of exercise in uniforms at 30 degrees C can result in losses of Na+ and Ca++ which exceed the normal daily intake of these electrolytes. Supplementation of fluid, Na+, and Ca++ appears to be warranted when scenarios require 6 h or more of uniformed exposure to heat.