Nutritional support is given to many patients in surgical intensive care after major trauma and serious sepsis but rarely after major elective surgery. We have quantified the changes in body composition that occur in these patients and have found that serious losses of body protein still occur after trauma and sepsis despite nutritional support. Correct nutritional management of critically ill patients in surgical intensive care depends on an understanding of the underlying physiology, drainage of sepsis, a high standard of general intensive care measures, and appreciation of sound principles of administration of intravenous nutrition.