The role of bile acids in the development of endotoxemia during obstructive jaundice was studied in rats. Endotoxin was not found in portal and peripheral plasma of control rats. The bile ducts of seven rats were ligated. On day 7 following bile duct ligation, six animals showed portal endotoxemia and five peripheral. Oral administration of sodium ursodeoxycholate reduced this frequency to 1/7 for portal plasma and 0/7 in the case of peripheral plasma. Subsequently the influence of a bile salt mixture (85% taurocholate, 15% taurodeoxycholate) on the binding and uptake of Salmonella abortus equi lipopolysaccharide by cultured rat Kupffer cells was studied. In control preparations, the percentage cell-associated lipopolysaccharide increased with time and reached a plateau after about 2 h of incubation at 37 degrees C. In the presence of 0.3, 0.6 and 1 mumol bile salts/ml the cell-associated lipopolysaccharide was about 5%, 13% and 29% lower, respectively, of that in control cultures. Tauroursodeoxycholate (1 mM) did not inhibit the lipopolysaccharide uptake by cultured rat Kupffer cells. Based on these observations, it is likely that both phenomena, i.e., (a) the low amount of bile acids in the intestines and (b) the high serum bile acid level, account for the high frequency of endotoxemia in the peripheral blood during obstructive jaundice.