1. Changes in liver glycogen and glycolytic intermediates were determined in ten patients undergoing abdominal surgery for carcinoma of the colon. 2. One hour of surgery resulted in a 19% decrease in liver glycogen, together with an increase in hepatic glucose 6-phosphate and glucose concentrations. 3. Blood glucose increased from 5.01 to 6.67 mmol/l during the hour between liver biopsies. 4. We conclude that the hyperglycaemia of surgery is associated with stimulation of hepatic glycogenolysis.