Nutrient modulation of inflammatory and immune function. The metabolic response to injury occurs after a diverse group of surgical injuries including major surgical intervention, shock, infection, and sources of inflammation such as pancreatitis. The response is mediated by the macroendocrine system, the autonomic nervous system, and the cell-cell communication system. The clinical manifestations include now well-described clinical, physiologic, and metabolic characteristics. The approach of aggressive source control, invasive circulatory resuscitation, and nutrition/metabolic support has been associated with an overall reduction in morbidity and mortality. In those patients who do not respond to this approach, the disease process progresses to multiple organ failure syndrome with its associated high mortality. Altering the route of feeding, preventing single nutrient and generalized nutrient deficiency, and reducing nosocomial infections with selective gut decontamination have not significantly altered the course or outcome of the disease process in this latter group of patients with persistent hypermetabolism. The available data support the position that this persistent hypermetabolism represents abnormal metabolic regulation resulting in persistence of the inflammatory response with associated suppression of the immune defenses. A number of research approaches are being taken to understand and modulate this abnormal state of regulation. Because of the role of specific nutrients in these regulatory processes, beyond their role in classic nutrition support, nutrients such as arginine n-3 polyunsaturated fatty acids, and RNA are being evaluated for their ability to modulate inflammation and to improve immune function. Preliminary results are encouraging. 