BILE salts are detergent-like molecules which occur widely in living systems. The dihydroxy and trihydroxy bile salts have an extraordinary ability to solubilize insoluble lipids such as phospholipids1–5, monoglycerides6 and long chain alkyl alcohols7. Lithocholic acid, a monohydroxy bile acid found in trace amounts in animals and man, has recently been found to cause pathological changes in liver when infused or fed in large amounts8–18. The intravenous infusion of sodium taurolithocholate to rats and hamsters results in severe cholestasis18. This can be prevented by infusing an equal molar amount of the trihydroxy bile salt sodium taurocholate. Feeding lithocholic acid to rats results in liver damage and gallstone formation, the latter the result of precipitation of sodium and calcium salts of glycolithocholate and its six keto derivatives8,9. Chickens receiving 0.2 per cent lithocholic acid and 2 per cent cholesterol in their diets develop severe liver necrosis and bile duct proliferation16, leading to hepatic failure and death.