UNLABELLED: The application of photosensitizers for inhibition of oxidative phosphorylation in order to temporally decrease oxygen uptake by tumor cells in the course of photodynamic therapy (PDT) evokes growing interest. MATERIAL AND METHODS: A photodynamic activity of MB and its combined use with chlorin e6 has been studied on the HeLa cell culture, their effect on cell metabolism in their co-accumulation and subsequent irradiation has also been assessed. RESULTS: MB generates reactive oxygen species in the cells in contrast to chlorin e6, which produces singlet oxygen. Besides, MB is converted to a colorless leucoform at low concentrations in the process of de-oxygenation. Incubation of cells with MB concurrently with chlorin e6 results in its greater fluorescence as compared to the incubation with MB only. MB concentration in the range of 1-10 mg/kg and the laser radiation dose of 60 J/cm CONCLUSION: The co-accumulation of MB with chlorin e6 prevents MB reduction to a colorless leucoform, decreasing the oxygen uptake by the cells and making it possible to use simultaneously type I and II photodynamic reactions.