The effect of aqueous and ether Chelidonium majus haulms extract on cervical HeLa tumor cells, mammary adenocarcinoma MCF 7 tumor cells and acute lymphoblastic leukemia CEM tumor cells in vitro have been studied. The purpose of this research was to compare the effect of aqueous and ether Chelidonium majus haulms extract on selected tumor cells. Colorimetric MTT assay have been used for the study of the antiproliferative effect of aqueous and ether haulms extract of Chelidonium majus on cell viability in vitro. The results of the experiments have shown the cytotoxic effect of the aqueous and the ether Chelidonium majus haulms extract on the individual tumor cells. The aqueous Chelidonium majus haulms extract was the most effective on CEM cells, it was less effective on MCF 7 cells and it was the least effective on HeLa cells. The ether haulms extract of Chelidonium majus was the most effective at all of studied concentrations on CEM cells and MCF 7 cells in comparison with HeLa cells, where it was significantly effective only at the highest concentration. Aqueous and ether haulms extract of Chelidonium majus tested in vitro indicated their cytotoxic activity. Both haulms extract of Chelidonium majus were more efficient on CEM cells. It is assumed that higher antiproliferative activity of ether haulms extract of Chelidonium majus is the result of higher antiproliferative activity of lipophilic substances. The lipophilic substances pass through membrane and bind to various proteins and change their biological activity., Vladimíra Tomečková, Veronika Tkáčová, Peter Urban, Marek Stupák, and Literatura