The effect of cooling the feet to alleviate heat strain was examined. Subjects, wearing chemical protective clothing, immersed their feet in water at temperatures of 10, 15, 20, 25, and 30 degrees C after sitting for 120 min at 35 degrees C. Heat lost via the feet ranged from 151 +/- 15 to 55 +/- 5 W, being greater in the colder water. In a second experiment, subjects wearing chemical protective clothing and specially designed water-cooled socks walked on a treadmill at 5 km.h-1 and 2.5% grade for 90 min at 35 degrees C. Four conditions were examined: no cooling, cooling throughout the walk, cooling during the last 60 min, and cooling during the first 30 min. Rectal and skin temperatures and heart rates were monitored. Cooling for the first 30 min had little effect on the measured parameters, however, when core temperatures rose to over 37.5 degrees C, cooling during the last 60 min significantly attenuated the increase in body temperatures and heart rates. We conclude that this method could be used to alleviate heat strain.