In many surgical departments it has been common practice to give patients with weight loss pre-operative parenteral nutrition before major surgery. The purpose of the present study was to elucidate the value of intravenous pre-operative nutrition in relation to the immune system. The study comprised 10 patients undergoing total gastrectomy. All patients had a weight loss of 15% of body weight or more within 6 months or 10% within 3 months. Before operation they all received parenteral nutrition for 1 week. They all had 1.5 g of protein per kg per day and energy corresponding to the basal metabolic rate + 50% as Vamin, Intralipid, and carbohydrate solutions. Before and after this treatment blood samples were taken to estimate neutrophil function (the rate of oxygen consumption and superoxide liberation, phagocytosis and intracellular lysis of Candida albicans, the concentration and consumption rate of ATP during phagocytosis, and chemotaxis) and immune globulins (IgG, IgM, & IgA). Cellular immunity (CMI) was estimated by intradermal application of seven different antigens. We found a significant increase in response to the intradermal antigens (p < 0.01) but no difference in any of the parameters expressing leukocyte function or immune globulins.