Multidrug resistance protein 2 (Mrp2) is an important transporter for biliary excretion of organic anions, and is reported to be up-regulated by dexamethasone. In the present study, effect of dexamethazone (1 mg/kg) on biliary excretion of bile acids and organic anions was studied in rats. After bile duct cannulation, bile acids and organic anions were intravenously administered, and their biliary excretion was studied. Biliary excretion of tracer doses of taurocholate and taurolithocholate-sulfate was unchanged with dexamethasone. Dexamethasone increased the excretory maximum of taurolithocholate-sulfate and sulfobromophthalein to 1.8 and 1.5 times, respectively, whereas it did not change the excretory maximum of phenolphthalein-glucuronide and taurocholate. Dexamethasone also increased biliary glutathione excretion. These results obtained by in vivo studies can be explained by the up-regulation of Mrp2, which had been reported in in vitro studies.