Study of 17 different areas of skin of 46 normal adults showed that there is a marked regional variation in the rate of sweating. The most rapid rates of insensible perspiration are from the hands, feet, forehead, and cheeks. The skin of the trunk, arms, and legs have relatively slow rates of insensible water loss. There are marked variations in the rate of insensible water loss for the same area from subject to subject and from time to time in the same subject. These marked variations result in overlapping of values for the various areas. Similarly, there are marked variations in the rate of sensible perspiration stimulated by a hot and humid environment. The rate of water loss increased often to a greater extent from those areas which showed relatively little insensible sweating when sensible sweating occurred, than from the areas which showed the largest rates of insensible water loss. There is no definite evidence of difference in the rate of insensible or sensible water loss during winter or summer mos. when the measurements are made under constant laboratory conditions. The rate of water loss from the skin of a subject resting quietly in bed is not materially increased when the temp. and relative humidity are increased from 75[degree]F. and 50%, respectively to 95[degree] and 75%. When the temp. is further increased to 100[degree]F., sweat literally pours. In a humid sub-tropical and tropical environment, when heat loss is interfered with, muscular exertion should not be maintained for prolonged periods of time.