BackgroundBreast cancer has been considered a public health problem and homeopathic treatments are becoming increasingly recommended due to its ways of action and absence of adverse effects. MCF-7 is an adenocarcinoma of human breast cell line useful as preclinicalmodel to screen therapeutic agents such as ultra-diluted Viscum album, an European plant which extract is commonly used in cancer therapy. AIMS MCF-7 and mesenchymal stem cells (MSC) were used to evaluate the in vitrocytotoxicity of homoeopathic Viscum album 1x10-3(VA3X). Methodscells were cultured for 24 hours in controlled environment (37.5oC and 5% CO2) in 96-well plates. After this time, VA3X was added to the culture medium in concentrations varying from 10 to 100 L/mL.A control group was maintained with culture medium only. Cells were cultivated for 48 hours in these conditions for evaluation of cell viability by MTT assay. ResultsHigher cytotoxicity was observed in MCF-7 when compared to MSC, as the lower concentration of VA3X was capable of inducing tumor cell death and not healthy cell death. The MTT assay results were that 42 L/mL of VA3X reduced MCF-7 cells viability to 50% and 62 L/mL reduced MSC cells to the same percentage, what means that tumor cells are more sensible to VA3X than heathy cells. ConclusionViscum albumpresented higher cytotoxic action on human breast cancer cell line culture than on mesenchymal stem cells. This medicine is extensively used against cancer, and the use of the homoeopathic form of it brings new possibilities as no or fewer adverse effects would be present.(AU)