Critically ill patients characteristically exhibit a pronounced catabolism in addition to a down-regulation of normal anabolic activity, leading to major complications from loss of body protein stores. The marked decrease in lean body mass and protein stores leads to the loss of essential structural and functional proteins required for restoring and maintaining homeostasis. The standard management of the catabolic response to injury and illness has centered on optimizing nutrient intake that modulates but does not reverse the process. Complications of ongoing catabolism therefore remain a major cause of morbidity. Addition of anticatabolic and anabolic agents that may counteract "the stress response to injury or illness" may be of significant clinical benefit. Agents currently available for clinical use, which will be described, can be divided into two groups. The first group are nutrients and nutrient metabolites, namely protein and the specific amino acids, glutamine, arginine, and branched chain amino acids, especially leucine. The second group are anabolic hormones, namely growth hormone, testosterone, and the testosterone analog oxandrolone. The pros and cons of these agents, as to their anabolic and anticatabolic value, are described.