Inter-individual differences in body temperature and resting metabolic rate (RMR), during comfortable temperature and mild cold were studied. Sleeping metabolic rate (SMR) was measured overnight at 22 degreesC and RMR the following morning at 22 degreesC and at 16 degreesC. Intestinal, rectal and skin temperatures were measured as well as the electromyography (EMG). The SMR and the RMR corrected for body composition were significantly related (p <0.001, r(2) = 0.57) which means that individual levels of energy expenditure during the night remained during the day. At 16C, the RMR increased without increase of EMG activity, indicating non-shivering thermogenesis. Gender differences exist for intestinal, rectal, pectoralis and hand temperature (p <0.05).