Surgery, trauma, burns and injury induce an inflammatory response that can become excessive and damaging in some patients. This hyperinflammation can be followed by an immunosuppressed state which increases susceptibility to infection. The resulting septic syndromes are associated with significant morbidity and mortality. A range of nutrients are able to modulate inflammation (and the associated oxidative stress) and to maintain or improve immune function. These include several amino acids, antioxidant vitamins and minerals, long-chain n-3 fatty acids and nucleotides. Experimental studies support a role for each of these nutrients in surgical, injured or critically ill patients. There is good evidence that glutamine influences immune function in such patients and that this is associated with clinical improvement. Evidence is also mounting for the use of long-chain n-3 fatty acids in surgical and septic patients, but more evidence of clinical efficacy is required. Mixtures of antioxidant vitamins and minerals are also clinically effective, especially if they include selenium. Their action appears not to involve improved immune function, although an anti-inflammatory mode of action has not been ruled out. Enteral immunonutrient mixtures, usually including arginine, nucleotides and long-chain n-3 fatty acids, have been used widely in surgical and critically ill patients. Evidence of efficacy is good in surgical patients. However whether these same mixtures are beneficial, or should even be used, in critically ill patients remains controversial, since some studies show increased mortality with such mixtures. There is a view that this is due to a high arginine content driving nitric oxide production.