Membrane transport proteins play a major role in hepato-biliary secretion of xenobiotics. Some of them, especially OATPs and OCT1, are present at the vascular pole of hepatocytes and mediate uptake of xenobiotics into parenchymal liver cells from blood whereas others, such as P-glycoprotein and MRP2, are ABC transporters present at the canalicular domain of hepatocytes and responsible for the transmembrane passage into bile of drugs or their metabolites. Many endogenous or exogenous factors, including drug metabolizing enzyme inducers, alter expression of hepatic transporters whose activity can moreover be inhibited by various structurally-unrelated compounds. Such changes of expression and/or activity of membrane transport proteins may contribute to some drug interactions.