The development of drug resistance during the therapy is a major obstacle in the successful treatment of various pathologies. The in vitro studies on cell lines have shown that exposure to a single drug often leads to a cross-resistance to several other structurally and functionally unrelated compounds. This phenomenon is known as multidrug resistance (multidrug resistance, MDR). The membrane transporters play a role in the absorption, distribution and elimination of metabolic products, of ions and of most drugs. The membrane transporters include a variety of membrane proteins with different structures and functions, such as, for example, exchangers of ions and proteins from the ABC family (ATP-binding cassette). Importance of the membrane transporters appears from genetic diseases that are caused by alteration of their functions. Although the role of membrane transporters in the drug effects aroused a particular interest in the recent years, the relevant transporters remain still unknown to most drugs. Even though it is known that a specific transporter interacts with a drug, there is the possibility that the unidentified transporters to recognize the same drug.