Twenty elderly patients having undergone colonic resection were randomized into two regimens of postoperative parenteral nutrition. Fructoglucose satisfied the basal caloric needs of the patients. Amino acids were given as a mixture that provided 0.11 (0.09-0.14; mean and range) g/kg/day of nitrogen only. In half of the patients the energy intake was doubled with fat emulsion. The mean nitrogen-energy ratios in grams of nitrogen/kcal/day were 1:201 and 1:336 in the two groups, respectively. Both regimens were given for three days, starting from the first postoperative day. On the first day, the mean nitrogen balance was negative in both groups. On the third day, the mean balance was slightly positive in the amino acid, fructoglucose plus fat emulsion group, but negative in amino acid plus fructoglucose group. Amino acid concentrations in plasma and urine were markedly elevated in both groups, but relative concentrations in plasma remained rather normal. Apparently, a positive postoperative nitrogen balance can be obtained with restricted amino acid supply, if energy is provided in abundance.