Malnutrition in surgical patients is associated with an increased incidence of postoperative mortality and morbidity. Preoperative nutritional support has been shown to be efficacious in reducing the incidence of these complications, although the postoperative complication rate in these patients continues to be greater than in their wellnourished counterparts. This study attempts to determine whether the postoperative course can be either influenced by or predicted from the preoperative response to nutritional support. Thirty-two patients with nutritional depletion who received an average of 1 week of total parenteral nutrition prior to a major abdominal operation were studied. These patients were followed for postoperative complications. Of the 16 patients who exhibited the characteristic response to early nutritional support, diuresis of the expanded extracellular fluid compartment with a resultant loss of weight (127.9 +/- 5.7 to 124.6 +/- 5.8 (SEM) lbs, p less than .001) and rise in serum albumin (3.21 +/- 0.14 to 3.46 +/- 0.15 gms%, p less than 0.001), only one developed a complication in the postoperative period. The other 16 patients did not exhibit this response. They retained additional fluid, gained weight (119.3 +/- 8.1 to 121.3 +/- 8.2 lbs, p less than .025), and showed a decrease in serum albumin levels (3.14 +/- 0.14 to 3.00 +/- 0.14%), p less than 0.01). Eight of these patients developed a total of 15 postoperative complications (p less than 0.01). This study demonstrates that the response to preoperative TPN is an important factor in assessing operative risk and morbidity. The need to individualize preoperative nutritional support and the timing of surgical intervention is clearly demonstrated.