1. Male golden hamsters were induced to hibernate. 2. During stimulated arousal (i) the time course of increase in deep body temperature was related to the time-course of increasing oxygen consumption and (ii) brown adipose tissue lipid content was determined at several time points. 3. In early arousal (0-30 min) more lipid was mobilised (14.6 kJ) than was utilised in metabolism (3.5 kJ). BAT lipids accounted for 88% of the total energy requirement of arousal (90 min). 4. We conclude that BAT not only supplies heat for arousal but fuel for other arousing tissues.