The relationship of body temperature and resting CO2 production was examined for the lizards Cnemidophorus velox and Sceloporus undulatus. The CO2 production of both species was characterized by broad temperature ranges (30-38°C) in which no temperature dependence of CO2 production was observed. Also, both species showed considerable betwee individual variability. The metabolic rate of the widely foraging species, C. velox, is significantly higher than that of the wait-and-ambush species S. undulatus. However, this difference is eliminated when the size of the animals and activity times are considered; both species then have similar estimated average daily energy costs.