Postoperative hypothermia initiates an increased oxygen demand in the postoperative period and may endanger patients with restricted cardiopulmonary reserves. In order to compare net heat losses and gains, we studied 28 women undergoing hip fracture surgery, using either general anaesthesia or spinal analgesia. The superficial and central temperatures were followed in the per- and postoperative period. Total body heat was calculated from temperature measurements. Temperature changes were unrelated to the type of anaesthesia. Large net heat losses occurred on transfer to the recovery room.