The social Damara mole-rat Cryptomys damarensis (124 g), has a mean (°SD) resting metabolic rate of 0.57°0.09 cm3 O2 g-1 h-1, within a thermoneutral zone of 27-31° C. This rate of metabolism is 43% lower than that predicted by the curve for rodents, and 29% lower than that predicted by the subterranean rodent curve. These data support the hypothesis that the resting metabolic rates of social and solitary subterranean rodents are lower than those of solitary species inhabiting mesic habitats. These low resting metabolic rates may represent an energy-saving adaptation to aridity. The energetic cost of burrowing, in relation to the dispersion patterns of food in arid habitats, may explain these low metabolic rates.