The effects of an elemental-enteral diet administered by a needle catheter jejunostomy or central total parenteral nutrition were prospectively studied in 15 patients undergoing abdominal operations. Infusions were started 1 day after operation and continued for 7 to 10 days. The two nutrient modalities were matched to deliver equal amounts of nitrogen and calories. Both promoted positive nitrogen balance and preserved body weight and serum proteins (albumin, transferrin, thyroxine-binding prealbumin, and retinol-binding protein). Both enteral and parenteral nitrogen caused a similar increase in plasma insulin levels. Pancreatic glucagon, total glucagon, gastrin, and pancreatic polypeptide were also maintained at similar levels in both groups. Plasma vasoactive intestinal polypeptide levels declined in patients receiving total parenteral nutrition but remained stable in the patients who were fed enterally. Both routes caused modest, inconsequential elevations in liver enzymes, but were otherwise equally safe. Patients tolerated total parenteral nutrition far better in the early postoperative period. Patients whose needs are great are probably better treated by total parenteral nutrition. Needle catheter jejunostomy feeding, however, is much less expensive. These studies do not support the commonly held belief that enteral nutrition is a more efficient route for administration of calories and protein.