Oxygen consumption ($\dot{V}_{O_{2}}$) and heart rate were measured at ambient temperatures between +20 and -40 C. Basal metabolic rate was 0.3 cm³/g·h (65 beats/min), the body temperature was 38 C, the lower critical temperature ($T_lc$) was 10 C, and conductance was 0.01225 cm³/g·h°C. Fat composition of 79 adult badgers captured during the winter showed maximal fat deposition of 31% body weight in November. Fat stores were reduced 37% between November and March. The burrow temperature remained between 0 and 4 C throughout the winter. Badgers in outdoor enclosures during the winter of 1977-1978 reduced their above-ground exposure by 93% from November through February. Two badgers remained below ground for more than 70 consecutive days during the 1978-1979 winter. While below ground, one telemetered badger entered a state of torpor, on 30 occasions, characterized by a 50% reduction in heart rate (from 55 to 25 beats/min) and a 9 C reduction in body temperature (from 38 to 29 C). The torpor cycle lasted an...