The results of several kinds of experiments have been introduced as evidence in support of the thesis that the thermoregulatory system of endotherms functions no differently in the presence of microwaves than it does in the presence of conventional sources of thermal energy. The thermoregulatory profile, unique for each species, provides the framework for the argument. The results of our experiments have demonstrated the equivalence between T and microwave intensity as they influence individual responses of heat production and heat loss. This equivalence, in turn, allows the prediction of specific alterations in thermoregulatory responses when microwaves are present. Predictions of this kind are possible because the hierarchy of autonomic responses available to any given species is always the same. This fact should provide some comfort to those who profess concern abut the uniqueness of absorbed radiofrequency energy and its fate within the body. Additional comfort can be derived from the demonstration that changes in thermoregulatory responses in the presence of microwaves depend upon the integral of energy absorption by the whole body, not upon energy deposited in some restricted locus such as the PO/AH. It is clear that the circulatory system plays a major role in the distribution of energy deposited during such exposures, a fact already emphasized by others (Burr and Krupp, 1980; Way, et al., 1981; Stolwijk, 1983; Krupp, 1983). This fact does not negate the presence of electrical hotspots as predicted on theoretical grounds (e.g, Kritikos and Schwan, 1979) or as demonstrated dosimetrically (e.g., Guy, 1971), but it does deemphasize their importance as potential deterrents to the efficient mobilization of thermoregulatory responses. The utility of the thermoregulatory profile in research of the kind described here cannot be overemphasized. Accurate profiles have been determined for most of the commonly-used laboratory animals as well as for human beings. In the broader sense, such profiles should serve as fundamental data to the design of any experiment in which microwaves may be present. For example, the normal "room temperature" for clothed human beings lies well below the LCT of most laboratory species and such a Ta may exert a substantial influence over diverse behavioral responses, drug effects, etc. as well as basic thermoregulatory responses (Adair, et al., 1983). This paper has demonstrated that by considering the thermoregulatory profile, microwave challenges to the thermoregulatory system assume their proper position within the fundamental science of thermal physiology.