A review of the literature on intracellular accumulation and distribution of anticancer drugs in sensitive and resistant tumor cells with the classic mechanism of multidrug resistance development, as well as on the role of ABC-transporters in the processes is presented. According to the data discussed the authors prove that clinical analysis of human tumor multidrug resistance phenotype always needs separate estimation of the functional activity of ABC-transporters, which control accumulation of MDR drugs in the cytoplasm and nucleus. The authors suggest a new term--"severity" of tumor phenotype of multidrug resistance.