OBJECTIVE To compare the caloric intake with the caloric requirements in postoperative patients being fed enterally via nasoenteric tubes, parenterally, or by both enteral and parenteral methods. METHODS Descriptive study. METHODS Surgical ICU in a university teaching hospital. METHODS Sample of 22 mechanically ventilated postoperative patients, mean age 62 +/- 17 yrs, selected from among those patients routinely scheduled to receive enteral or parenteral nutrition or both, for greater than or equal to 4 days. The patients were studied for a total of 144 study days. METHODS Eight patients received total parenteral nutrition, eight patients received enteral nutrition, and six patients received both parenteral and enteral nutrition. METHODS Resting energy expenditure was measured by using indirect calorimetry, and daily nutritional intake was quantitated. RESULTS The patients who received parenteral, or enteral plus parenteral nutrition received an average of 80% of their caloric requirements, while those patients who received only enteral nutrition received only 68% of their caloric requirements. There was more day-to-day variation in nutrient intake in the enteral group (40% +/- 56%) than in the parenteral group (12.2% +/- 24%, p less than .001). CONCLUSIONS Enteral nutrition delivered via nasoenteric tubes as the sole delivery method in postoperative critically ill patients resulted in an inadequate and inconsistent nutrient supply. The use of parenteral or parenteral plus enteral nutrition resulted in more stable and adequate feeding than feeding by enteral nutrition alone.