The degree of pleasantness or unpleasantness of thermal sensation aroused by a particular peripheral thermal stimulus has been shown to be an indicator of thermal state of the body in relation to the thermoregulatory set point. This phenomenon is known as thermal alliesthesia. The quantification of thermal alliesthesia was possible using two methods: (1) A set of temperature stimuli (15, 20, 25, 30, 35, and 38‡ C) was applied, by means of a Peltier thermode 5.5×2.7 cm2, on the back of the hand, the forehead, and the back of the neck. When each stimulus had been applied for 5 s the subjects voted their degree of thermal pleasantness/unpleasantness on a psychophysical scale ranging from +2.0 for very pleasant to −2.0 for very unpleasant. (2) The subjects were also asked to adjust the Peltier thermode temperature, without looking at the temperature scale, such that the temperature (on the back of the neck) was maintained at the level the subjects considered most pleasant. The subjects also rated their general thermal comfort sensation on a five point scale ranging from +2.0 for very comfortable to −2.0 for very uncomfortable. Rectal temperature and skin temperature at eight locations were continuously recorded. Passive thermal exposures (54) were made with nine passive subjects and 42 exposures were done with working (50 watt) subjects. All exposures were carried out in a climatic chamber at a constant temperature, relative humidity (45%), and air speed (0.3 m/s). Each subject underwent 6 exposures at six room temperatures of 15, 20, 25, 30, 35, and 40‡ C. The results of work exposures confirmed the findings of previous studies; namely, the effect of core temperature change overrides any effect due to mean skin temperature on alliesthesial response. A mathematical function to predict the mean slope of the thermal pleasantness rating/stimulus line (a measure of the alliesthesial response) was derived using the data obtained from the passive thermal exposures. The results indicate that alliesthesial response can be used as a quantitative indicator of thermal stress.