P-glycoprotein (Pgp) is an ATP-dependent efflux pump extracellularly transporting a variety of compounds. It influences bioavailability, disposition and excretion of many drugs as well. Its major localizations are in intestinal, hepatic, renal epithelial cells and hemato-encephalic (blood-brain) barrier and therefore it is considered as an important defence mechanism of the body against xenobiotics. Pgp is a protein product of MDR1 gene, whose overexpression and causing high activity of Pgp in cancer cells and represents one of the mechanisms of multidrug resistance to anticancer therapy. Several single nucleotide polymorphisms have been identified in the MDR1 gene and their functional importance is being intensively studied. This article reviews recent knowledge of the structure, structural specifity of Pgp, and functional significance of several MDR1 polymorphisms.

        Key words: MDR1, P-glycoprotein, transporter, polymorphism, multidrug resistence.