Background: Anaesthesia and surgery reduce the clearance of glucose. We studied how surgical procedures of different magnitude affect the clearance of a glucose load. Methods: An intravenous infusion of 10 ml/kg/h of 2.5% buffered glucose was given over 80 min to 26 patients with a mean age of 50 years. The infusion started with the skin incision during minor surgery (inguinal hernia repair), medium-range surgery (laparoscopic cholecystectomy) and major surgery (aortic surgery, gastrectomy or colorectal surgery). General anaesthesia was induced in all patients and was supplemented by thoracic epidural analgesia for those undergoing major surgery. Plasma glucose was measured repeatedly for comparison of the clearance and endogenous glucose production during and after the infusion. Results: Metabolic changes affected the shape of the plasma glucose curves more than the peak values. In those undergoing minor surgery, the clearance after the infusion was 65% of that recorded during the actual administration of glucose. The corresponding values for medium-range and major surgery were 37% and 60%, respectively (P < 0.001). The limited decrease in clearance in major surgery can probably be attributed to the epidural analgesia. In all three groups, the estimated endogenous glucose production decreased by the same magnitude as the clearance. The volume of distribution for glucose averaged 10.3 l. Conclusion: The hyperglycaemic effect of anaesthesia and surgery was not fully expressed within 80 min, regardless of the extent of surgery, and therefore appears to develop slowly. Even minor surgical trauma affected the metabolism of glucose.