Rate of oxygen consumption was measured in two female sloth bears, Ursus ursinus, at ambient temperatures of 9–38.5°C. Their basal rate of metabolism is low by all standards, as might be expected from their myrmecophagous and frugivorous habits, but is similar to that found in the omnivorous North American black bear, U. americanus. Vertebrate-eating bears, in contrast, have higher basal rates, even when denning. The thick fur coat of the sloth bear may partly compensate for its low basal rate. All differences in basal rate among large ant- and termite-eaters cannot be understood in terms of our present knowledge of ecological relations.