The Sphenomorphus quoyi species complex (Lacertilia: Scincidae) of southeast Australia consists of three lizard species, distributed as continuous but largely allopatric populations, and a fourth species which has a disjunct distribution at high altitudes within the range of the other three. The four species have similar Voluntary temperatures (range of body temperatures within which normal activity occurs) despite the fact that they occupy different geographical areas.Altitudinal zonation is shown in the distribution pattern of the four species with S. quoyi and S. tympanum (warm temperate) restricted to the lower altitudes. The level of the mean daily minimum and maximum temperatures are different in each of the four species distribution areas. Similarly, the area occupied by each species is characterized by different daily sunlit and shade surface temperatures and different duration of ground surface subzero temperatures. Floristic composition of the four areas and the basking sites utilized by each species are also dissimilar.The lower temperature tolerances and the acclimation range of the Critical Minimum temperatures of S. quoyi and S. tympanum (warm temperate) exclude these species from the higher altitudes with the relatively lower environmental temperature levels. The Critical temperatures of the species which are found at high altitudes, do not explain why sympatry is not found with the lowland species.