When acclaimated for two months at 26 C the social Mashona mole-rat Cryptomys hottentotus darlingi (±S.D.) resting metabolic rate (RMR) of 0·98±0.·14cm2O2g -1 h-1 (n=21), within a thermal neutral zone (TNZ) of 28 31·5 C ambient temperature (Ta). The body temperature (Tb) of the mole-rat is very low. 33·3±0·5 C, and remained stable between 25 31·5 C (n=28). Above 33 C. Tb increased to a mean of 34·±0· C (n=28) (Ta range 33 39 C). Below Ta 25 C. Tb showed strong poikilothermic tendencies, with Tb dropping to a mean of 26·8±1·16 C. whereas above Ta25 C. Tb varied in a typically endothermic pattern. The conductance is high 0·19±0·03 cm2 O2g1 C 1 (n=28) at the lower limit of thermoneutrality. The mean RMR at 18 C (the lowest Ta tested) was 2·63 ± 0·55 cm3 O2g 1 h 1 (n=7) which is 2·6 times that of the resting metabolic rate in the TNZ.