Abstract : The influence of bile acids and bile acid derivatives on the rate of excretion of free cholesterol (FC) and phospholipid (PL) in bile produced by the isolated perfused rat liver has been demonstrated. The livers were perfused for 60 minutes to eliminate preformed bile acids from the perfusion system, then various bile salts were infused at a constant rate of 10 mg per hour for an additional two hours. Bile samples were collected throughout and analyzed for FC and PL. Each of the bile acids or derivatives tested was effective in stimulating lipid excretion. Thus, it was shown that not only were the bile acids normally produced by the liver (taurocholic and chenodeoxycholic acids) effective in stimulating bile lipid excretion, but so also were deoxycholic and lithocholic acids. These latter acids, derived only by bacterial action, absorbed from the intestines and returned to the liver, may play an important role in the response of the liver to ionizing radiations which markedly affect bile acid absorption and metabolism. (Author)