The very limited information concerning the physiological capacities and adaptive potential of females to heat strain and work suggested the need to interrelate the levels of certain specific circulating hormones to the physiological responses and adaptative qualities of women subjected to this combination of stresses. It is proposed to make cross-sectional studies of the influence of these variables in women under a variety of combinations of heat strain, work loads, and exercise duration. Acclimatization of females to work in the heat, as well as at rest, will be studied. These studies will consider temperature regulation, circulatory adjustments, capacity of sweat glands to produce sweat, the electrolyte composition of the sweat, and changes in plasma volume. They are designed to increase our understanding of the differences between men and women in terms of their functional capacities and adaptive potentials.