Surgery performed during general anaesthesia has been shown to induce an increase in oxygen consumption. It is postulated that this response might be influenced by the surgical procedure performed. Metabolic gas exchange was continuously measured by indirect calorimetry for 30 min in 45 patients undergoing four different surgical procedures during general anaesthesia with propofol/fentanyl/vecuronium as follows: elective laparotomy (n = 13); emergency laparotomy (n = 10); elective knee joint arthroscopy (n = 10); gynaecological laparoscopy (n = 12). A significant increase in oxygen consumption occurred in all the groups within 5 min of skin incision. The greatest increase was seen in those undergoing elective laparotomy (+13%, p < 0.001 at 15 min), with similar smaller increases in the other three groups (+6 to +7%, p < 0.05). Surgery induced an increase in systolic blood pressure in all four groups, being most pronounced in the elective laparotomy group (+47% 15 min after skin incision, p < 0.001). These patients also experienced a significant rise in heart rate (+14%, p < 0.01 at 15 min). Carbon dioxide production increased both in the laparoscopy patients (+9%, p < 0.05) and, transiently, in the elective laparotomy group (+6% at 15 min, p < 0.01), but decreased in the other two groups (-7 to -15%, p < 0.05). Surgery induced a parallel increase in both oxygen consumption and systolic blood pressure in all types of operations, although the magnitude varied. Continuous measurement of metabolic gas exchange may provide an additional method of evaluating the metabolic response to different types of surgery.