Standards for the protection of workers in hot industries are based primarily on laboratory studies in which male subjects worked continuously in a hot environment. The purpose of this study is to examine thermoregulatory and cardiovascular responses to a more realistic situation, work in the heat and rest in a cool environment. The data will also permit an evaluation of the "prescriptive zone" as an environmental heat standard during intermittent work and when the energy requirement of the job is expressed relative to the cardiovascular fitness (VO2 max) of the worker. Women have been selected as subjects since there is still relatively little information on how females respond to the challenge of working in hot environments. Subjects will work either continuously or intermittently in environments ranging from 20-32 degrees Centigrade CET at work loads approximately 30% and 5 of their maximal aerobic power (VO2 max). During intermittent work the subject will rest in a cool environment. Total energy expenditure during the 120-min intermittent and continuous work sessions will be equal. At each CET there will be two ambient conditions, one with a high radiant load and a low vapor pressure and the other with a low radiant loadand a high vapor pressure. Physiological variables being considered include metabolic, temperature, sweat and cardiovascular responses. The results of this study will provide iformation needed in setting realistic environmental standards for hot industries and at the same time answer the basic physiolgoical question: Can the thermoregulatory and cardiovascular systems inegrate the varying environment and job during long-term work?