Oncologic diseases are among leading cause of mortality in developed countries. Despite significant progress, the use of standard cytotoxic chemotherapy has reached a therapeutical plateau. Currently, the process of selecting chemotherapy represents a trial and error method neglecting biological individuality of tumor and its bearer. The improvement of treatment results is expected from ex vivo drug sensitivity testing which may allow to choose the most effective drug for individual patient and to exclude agents to which the tumor cells exert resistance. New techniques and rapidly increasing knowledge about the molecular basis of malignant diseases provide important opportunities for the future of chemotherapy. This paper reviews current methods used to test the resistance of tumor cells to a panel of anticancer agents in vitro. In addition, we focused on the in vitro MTT assay which represents one of major technique for testing of tumor cell resistance to anticancer agents.