In this paper we present analysis of living cells response to photodynamic treatment. Intracellular generation of reactive oxygen species was performed by means of Radachlorin photosensitizer. Radachlorin accumulation in cells was controlled using fluorescence microscopy. Digital holographic microscopy was applied for monitoring cells response to photodynamic treatment at different doses. The results obtained can be used for estimation of cells resistivity to intracellularly generated reactive oxygen species.