The study is aimed at evaluation of in vivo biliary and renal excretion of rhodamine 123 (Rho123), a P-glycoprotein substrate, in rats during either acute or chronic cholestasis induced by bile duct obstruction. The employed methods involve both in vivo determination of pharmacokinetic parameters of Rho123 after experimentally induced cholestasis, and following expression studies (quantitative immunohistochemistry and Western blot).