Department of Biochemistry and Cytochemistry examines the development of multidrug-resistant leukemia cells and ways to influence the process of multidrug resistance. The most common cause of multidrug resistance is increased expression of transporter proteins of the ABC gene family of membrane transporters. These integral proteins of the plasma membrane of animal cells have the ability to remove cytotoxic substances from intracellular space, so they can protect cells from the toxic effects of environmental stress. In tumor cells, the amount of ABC transporters is sometimes excessively increased under the influence of treatment, resulting in decreased efficiency of antitumor drugs and in preventing chemotherapy. Knowledge of regulatory processes involved in this process has a potential to improve pharmacotherapy of certain cancers and thus economy of their treatment.