Abstract Sequential changes of body temperature have been measured for 48 h in 147 patients after major elective abdominal, cardiac, orthopaedic and pelvic surgery. Core temperature (aural canal) started to increase immediately after surgery reaching a mean peak value of 37·5°C 14 h (range 8-16) after the end of surgery. Subsequently, a second peak of 37·4°C was shown 18 h (range 16-20) later. The time interval between these two peak temperatures was constant for all types of surgery studied. A close examination of core temperature oscillations during a 72-h postoperative period and a comparison with a pre-operative 24-h cycle in a group of 14 patients who underwent cardiac surgery did not show any circadian rhythm. In the third part of the study, analysis of postoperative body temperature and metabolic rate showed a similar pattern of increase for core and mean skin temperatures, and oxygen consumption.