The thermal relations of reptiles have been extensively analyzed in both field and laboratory during recent years. Although fundamentally poikilothermic, many of these animals behaviorally achieve some control of their body temepratures during activity. Now that a wealth of descriptive information is available on the thermal relations of reptiles, it has become feasible to complete several analyses that are fundamental to the full characterization of the thermobiology of this group. The first of these involves quantification of the heat exchanges of various species in nature and under precisely controlled conditions in the laboratory....The second type of analysis required concerns the peripheral and central neural mechanisms controlling the various facets of reptilian thermoregulation....Finally, we need to evaluate fully the physiological consequences of operation at the preferred body temperature for species having well-defined thermal preferenda. Although it appears reasonable to assume that a correlation exists between the general thermal adjustments of such reptiles and their preferred body temperatures and that various physiological processes reach optima at or near these temepratures, analysis of these adjustments and identification of the processes has proceeded very slowly. However, recent work has provided some new insights concerning these relations. It is with these that this reveiw will deal.