Effect of an intraperitoneal injection of cimetidine at a daily dose of 160 mg/kg for two weeks on biliary lipid secretion, fecal excretion of bile acids and intestinal bile acids was studied in rats. Bile flow, biliary lipid secretion and fecal excretion of bile acids remained unchanged, while the pool size of bile acids decreased by cimetidine treatment. Chenodeoxycholic acid increased with a concomitant decrease of beta-muricholic acid in the biliary bile acid composition of cimetidine-treated rats.