Control of infection in the surgical intensive care unit demands unfailing attention to three distinct areas: a) The bacteria responsible may be endogenous or exogenous. The effects of the former can be limited by careful surgical techniques and judicious use of antibiotics, of the latter by the practice of asepsis and antisepsis, essentially of scrupulous cleanliness. b) The environment of infection concerns the support of natural barriers to infection (notably the integrity of the skin and the adequate drainage of the pulmonary system), and the sterility and appropriate care and use of the many invasive devices currently available. c) The patient's natural defence mechanisms show considerable variation, and those at increased risk can be detected by skin-testing with a number of antigens as well as by recognized clinical features. It is in these patients with anergy and abnormal natural defences that total parenteral nutrition can be of the greatest value.