['Various effects on tumor cells have been described for zoledronic acid (ZOL). However, only limited data exist regarding its influence on the motility of tumor cells. Since migration of tumor stem cells is a decisive step in metastasis, we examined whether ZOL reduces their motility.', 'We investigated the effects of ZOL on stem-like progenitor cells obtained via the formation of spheroids from the human breast cancer cell line MDA-MB 231. Stem cell properties were verified by measurement of high CD44 expression and absence of CD24 expression. Motility was explored by time-resolved videography, protein expression by western blotting.', 'ZOL strongly reduced the migration of stem-like progenitor cells. Cellular velocity was reduced by 61% following exposure to 1 μM ZOL and by 82% after exposure to 10 μM ZOL. Accumulated distance traveled by the cells was reduced by 60% and 79% after exposure to 1 μM and 10 μM ZOL, respectively. The remaining cellular motility led to very little change in distance, with cellular activity appearing more as "stepping on the spot". The reduced motility might be due to reduced phosphorylation of focal adhesion kinase (FAK), an important enzyme in cellular migration.'] Does zoledronic Acid inhibit the Motility of Cancer Stem-like Cells from the Human Breast Cancer Cell Line MDA-MB 231?