Survival times of Australian lizards representing 29 species of 16 genera in the Agamidae, Scincidae, Gekkonidae, and Pygopodidae, were determined at a series of high temperatures in the range in which this function shows strong thermal dependence. Most species were studied at 40.5°, 43.5°, and 46° C, but this range was expanded to include 37.5° or 47° C for a few. Results indicate some differences in heat resistance between congeneric species and numerous differences of this type between representatives of different genera. The most conspicuous differences in heat resistance between members of different genera are those involving different families. Agamids are notably more heat resistant than skinks and pygopodids. Within a family, the largest variations in thermal tolerance are evident among the genera of geckos studied. Members of some (Heteronota, Phyllodactylus, and Phyllurus) were less tolerant than the majority of skinks, whereas members of other genera (Diplodactylus, Gehyra, and Rhynchoedura) approached the agamids in heat resistance. Intergeneric variations in heat tolerance closely parallel the differences in preferred body temperatures of these lizards (measured in laboratory thermal gradients), independent of their geographical distribution. However, the body temperatures of lizards active in nature are not always the same as the preferred temperatures, and the heat tolerances of the five species of Amphibolurus, which have similar preferred temperatures, correlate well with the levels of body temperature at which they are active in nature. These latter differences are associated with the geographical distribution of the species.