The efficacy of parenteral protein alimentation in the postoperative patient remains in dispute in spite of many pertinent studies reported in the medical literature. Information which is available strongly points to significant nitrogen sparing attributable to the use of intravenous protein digests, but rigidly controlled balance studies in postoperative patients have not been described. The present investigation is directed toward this purpose. We have made a comparison of parenteral protein feedings with isocaloric oral protein feedings as well as with protein-free parenteral feedings by means of nitrogen balance measurements. The results of this study indicate that parenteral protein feeding is almost equivalent to an identical oral protein feeding in nitrogen sparing. Both oral and parenteral protein feedings cause marked increases in nitrogen balance when compared to isocaloric, protein-free parenteral feedings. While nitrogen sparing may not be of obvious benefit for short periods, prolonged nitrogen losses or the excessive nitrogen losses