Glucose and fluctose (400 g/24 h) were compared as sources of carbohydrate in parenteral nutrition in patients following major abdominal operations or following multiple injuries. Group A (n = 8) received glucose during the first 2 days and fructose for another 2 days thereafter. In group B (n = 8) the sequence of carbohydrate infusion was reversed (2 days' fructose follwed by 2 days' glucose). The additional infusion to amino acids and a fat emulsion remained constant (total calories: 2,700 kcal/24 h). The following results were obtained: 1. Mean blood glucose concentrations were elevated in both infusion periods. During infusion of glucose the values were about 10% higher than those obtained during fructose infusion. Insulin administration was not necessary any of the patients studied. 2. Urinary excretion of both monosaccharides was negligible. 3. Blood lactate concentrations were higher during the infusion of fructose when compared to the glucose infusion period. The concentration of ketone bodies in the blood was not significantly influenced by either regimen. No major changes in base-acid equilibrium were observed. 4. The serum concentration of uric acid and several other metabolites did not differ significantly during the two infusion periods. 5. Mean urinary urea excretion exhibited a 30% increase during fructose infusion when compared to the glucose infusion period (p less than 0.012). From the results of t;is study and earlier findings it is concluded that fructose in a dose up to 400 g/day has no proven advantages over glucose in postoperative parenteral nutrition.