A computer program has been developed which predicts an individual's physiological responses to various combinations of environment and exercise. The user enters information concerning the individual (height, weight, age, etc.), the environment (dry bulb temperature, air velocity, etc), the task (sit, walk, metabolic rate, etc) and the simulation (for 50 min, output every 10, etc). The program then predicts body temperatures, heart rate, sweat rate, comfort, etc and prints it out at the desired times. An important feature of the program is that variables can change during the simulation. For example, the task can change from sit to walk, the temperature from 30 C to 45 C, etc. The article gives an overview of the program and compares predictions vs data for some situations.