Radio-telemetric monitoring of 70 free-ranging carpet pythons (Morelia spilota imbricata) at two sites in southwestern Australia provided extensive data on the body temperatures exhibited by these animals. The snake's thermal regimes were affected by season, time of day, location, microhabitat, size and sex, behaviour, and reproductive state. Over most of the year pythons exhibited relatively smooth unimodal diel curves of heating and cooling, attaining maximal temperatures around 30°C. The (small) male snakes heated and cooled more rapidly than did the (larger) females. Climatic differences between our two study sites generated substantial shifts in mean body temperatures and thus, in the diel timing of ambush foraging behaviour. Females wrapped tightly around their eggs after oviposition and brooded them throughout the ensuing 8-week incubation period. Throughout this time, females were facultatively endothermic, maintaining high constant temperatures through shivering thermogenesis. Females nesting in sites with relatively poor thermal buffering (under rootballs of fallen trees rather than rock crevices) supplemented endogenous heat production with occasional basking, and hence overall maintained lower and more variable incubation temperatures than did females with "better" nest sites.