The effects of continuous lumbar epidural analgesia and general anaesthesia with artificial ventilation upon body temperatures were studied by measuring aural, nasopharyngeal, deltoid skin, calf and big toe temperatures in 33 patients subjected to open prostatectomy. The patients were randomly allocated to two groups. 17 were allocated to epidural analgesia, during which the rate of temperature decrease was slight and lasted about two hours. 21 were allocated to general anaesthesia, during which the core temperature fell relatively steeply for four hours. The resulting difference in core temperatures between the groups was statistically significant (P less than 0.05). Consequently the number of patients with core temperatures below 35 degrees C was significantly higher after general anaesthesia than after epidural analgesia (11 vs. 1; P less than 0.01). Seven of the 17 epidural patients (41%) shivered during the latency period of the blockade or operation. Two of the 21 general anaesthetic patients (10%) shivered later in the recovery room. There existed no relationship between shivering and the core temperature. The general anaesthetic patients showed a significant negative correlation between the body mass index (body weight (kg)/height (m2)) and the decrease in core temperature indicating a protective function of the fat layer against heat loss. After epidural analgesia no such correlation was found.