Patients undergoing major gastrointestinal surgery who had a prognostic nutritional index (PNI) score of greater than 30% were randomized to receive a preoperative course of 10 days of intravenous nutrition or to undergo surgery at the next convenient operation list. Two groups of 17 patients were well matched for age, sex, and nutritional status. Although they underwent diverse operations, the extent of these was similar: 12 +/- 3 days of parenteral nutrition resulted in weight gain, 3.2 +/- 2.3 kg p less than 0.01; increased triceps skinfold, 0.6 +/- 1.2 mm p less than 0.05; improved immunological state, p less than 0.02; and improved PNI, 5.5 +/- 10.1% p less than 0.05. The changes in serum albumin and transferrin were not significant. There were only three major complications with one death in the treatment group but this was not significantly different from the control group which had six major complications and three deaths. This study suggests that patients with demonstrable nutritional depletion who require major gastrointestinal surgery will benefit from a preoperative course of parenteral nutrition, but to conclusively prove this a large and probably multicentre study will be required.