The normal body temperature level in the nine-banded armadillo varies between 34.0° to 36.4° C, showing diurnal fluctuations up to 2.4° C. The responses to cold exposure included a rise in deep rectal temperature resulting from reduced heat loss by vasoconstriction with a later increased heat production by progressive shivering. Values for oxygen consumption were from 200 to 275 cc/kg/hr at 30° air temperature, increasing to 1400 cc/kg/hr at -10° C air temperature. At elevated air temperature, heat loss was increased by vasodilation and panting. After 8 hours of exposure to specific air temperature, there was no net decrease shown in rectal temperature at 0° C air temperature. At -10° C air temperature, the tolerance time averaged from 3 to 5 hours and was closely associated with the behavior of the animal. The over-compensation observed in the armadillo to a cold stress indicates well-developed mechanisms for reducing heat loss and increasing heat production. The development of central nervous thermostatic control of these mechanisms seems to be the limiting factor to higher efficiency of homeotherapy in the armadillo.