We investigated the postoperative metabolism of patients undergoing gastric operation by beginning total parenteral nutrition pre- (group 1) and postoperatively (group 2). A third group remained fasting until 3 h after the surgical intervention. Because of the high serum glucose concentrations and the high glucose losses in the 24-h-urine on the operation day in group 1 and 2 only the basic glucose requirement (150--250 mg/24h) should be given in the early postoperative period. The low blood glucose concentration in group 3 and the elevated lactate values in group 2 underline this recommendation. Compared with group 2 and 3 group 1 had low free fatty acid concentrations of 250 muVal/l because of the continuous pre-, intra-, and postoperative infusion. Compared with normal metabolic conditions the free fatty acids don't seem to have the same insulinantagonising effect in the posttraumatic state. The fall of cholesterol after the surgical trauma reached its maximum after 12--15 h and amounted to about 40mg% in the first two groups. Albumin and total protein fell continuously in group 1 and 2. The electrophoresis in group 1 showed a rise of alpha 1-, and alpha 2-globulin to more than double the initial value, the beta-globulin showed only slight changes, the gamma-globulin dropped only slightly up to the 4th postoperative day. As a sign of an augmented catabolism the serum urea concentration rose during the postoperative state. Group 1 and 2 had a favourable nitrogen balance. The postoperative bilirubin rise could be held lower in group 1 compared to group 2.