The barrier function of the gastrointestinal tract may be assessed in a number of different ways. The intestinalpermeability test is a non-specific and indirect test, while measuring bacterial or endotoxin translocation is a more direct test of barrier function. Studies demonstrate that an increased permeability and bacterial translocation may result from free radical damage to the mucosal surface and occurs directly through morphologically intact enterocytes. Total parenteral nutrition is often associated with bacterial translocation but this may be independent of the development of an atrophic intestinal mucosa. In critical illness splanchnic perfusion is an important determinant of intestinal mucosal integrity and nutritional studies in this setting have variable outcomes as there are many other confounding factors that affect the barrier function of the intestine. The clinical consequences of bacterial translocation may include postoperative sepsis but the progression to multiple organ failure (MOF) has not been demonstrated. While it seems likely that a persistent inflammatory response in a patient may lead to the development of MOF, it is not necessarily true that such a persistent inflammatory response will result from the translocation of bacteria or bacterial products across the intestinal wall.