Philadelphus coronarius L. is big, leggy and deciduous old-fashioned shrub known for its fragrant white flowers in the late spring. Some members of genus Philadelphus L. are known for their antibacterial, antiradical and immunomodulatory effects. Therefore, these herbs represent prospective sources for the isolation of active substances with desired effects. We have investigated the cytotoxicity effects of water extracts from leaves and branches of Philadelphus coronarius L. (Hydrangeaceae). A431 cells (human skin carcinoma cell line) and the human breast adenocarcinoma cell line (MCF-7) were treated with various doses of individual extracts (0,1-100 microg dry matter/ml) for 24 h and 72 h. The highest toxic effects of both plant parts extracts were observed on MCF-7 cells regardless the time of treatment. Cells A431 were less sensitive to toxic effects of leaves and branches extracts but the time dependence was present with the tendency of increased toxicity after chronic treatment. There were no differences in the extent of toxic effects between branches and leaves extracts. The results obtained so far will provide the basis for the future studies with isolated active substances from these extracts.