Surgical treatment of patients with obstructive jaundice is associated with a high postoperative morbidity and mortality. A correlation was suggested between endotoxins and the observed complications. The mechanism by which endotoxins affect the negative outcome in operated jaundiced patients was, however, not clear, nor was the mechanism of clinically used preventive treatments. Several experiments were therefore performed in rats with biliary obstruction, to investigate whether and how endotoxins are active. The role of endotoxins was studied in a model in which endotoxins were absent. In germfree rats (free of bacteria and thus of endotoxin) the effect of biliary obstruction was studied and compared with biliary obstruction in conventional rats. To substantiate further the role of endotoxin, anti-endotoxin treatments (oral lactulose or internal drainage) were tested in rats with obstructive jaundice undergoing a severe surgical trauma. It is shown that endotoxins are responsible for complications (suppression of cellular immunity, kidney function, mortality) and that these complications can be prevented with an anti-endotoxin treatment. These results may have implications for preoperative treatment of jaundiced patients.