In recent months, numerous reports concerning total parenteral nutrition in critically ill patients have been published, including the guidelines and recommendations of the American Society for Parenteral and Enteral Nutrition. The old controversy regarding the use of the enteral versus parenteral route still exists. Although the enteral route is indicated in those patients with normal gastrointestinal function, the parenteral route is obviously beneficial in several clinical conditions and appears to be associated with few procedure-related complications when performed by experienced clinicians. There is also continued interest in the supplementation of parenteral formulas with nutrients that were previously considered nonessential, such as arginine, glutamine, and omega-3 fatty acids, but that may become essential in the setting of critical illness.