Concerns have recently been expressed at suggestions that postoperative sepsis may be more common in patients who have received preoperative total parenteral nutrition (TPN). The mechanism suggested for this is that TPN causes intestinal mucosal atrophy leading to increased bacterial translocation from the gut as a source of systemic sepsis. This hypothesis was examined in 203 patients who had an elective laparotomy, 28 of whom required at least 10 days of preoperative TPN. Neither mucosal atrophy nor bacterial translocation was more common in parenterally fed patients than in enterally fed controls. In humans theoretical concerns about the adverse effects of TPN on intestinal integrity are unfounded.