An increasingly large number of dietary components have been found to alter immune system function and, therefore, may be considered to have a pharmacologic effect (pharmacologic nutrition). Those dietary factors which have already been shown to influence outcome by producing a pharmacologic effect rather than correcting or preventing a simple deficiency include proteins (both type and amount), arginine, glutamine, omega-6 and omega-3 fatty acids, short-chain fatty acids, the metals iron and zinc, and the vitamins E, C, and A. Therapeutic outcome has already been influenced by dietary therapy (pharmacologic nutrition) in patients after burn injury or who have vascular diseases, and in experimental animals for the prevention of gut origin sepsis, the prevention and treatment of infection, prevention and development of secondary lesions in autoimmune diseases, augmentation of immunosuppression in transplantation, and in the treatment of cancer. Nutritional therapy using disease-specific formulations or supplements is an old idea now undergoing rapid evolution to increasing importance for successful therapeutic outcome.