The purpose of the present paper is to develop an environmental temperature scalebased on our current knowledge of the physiology of heat reguIatlon as it applies to comfort, temperature sensation, and health. We will construct this scale by using first the heat exchange equations during the passive state as a rational starting basis and by introducing then the effect of known physiological regulatory controls. The principles to be described may be applied to many levels of activities, to various air movements, and to radiant heating and cooling. However, our present discussion will deal primarily with normally clothed sedentary human subjects in a uniformly heated and normally ventilated environment. As a numerical index, the new temperature scale will be defined in terms of dry bulb and normal humidity and will be comparable to temperatures of natural environments, which one generally experiences in temperate climates.