In this study information was obtained on bioavailability of genistein, daidzein and their glycosides in human intestinal epithelial Caco-2 cells grown on semi-permeable filters. The integrity of Caco-2 monolayers was confirmed by transepithelial electrical resistance measurements and by determination of the permeability of the radioactive marker polyethylene glycol (PEG4000). After 6 h approximately 30–40% of genistein and daidzein added at the apical side was transported to the basolateral side and this level was maintained for 24 h, The glycosides were barely transported through the Caco-2 cells. No significant metabolism of genistein and daidzein in the Caco-2 cells occurred, whereas the glycosides were mainly metabolised to their respective aglycones. Obviously, our data indicates that Caco-2 cells contain an endogenous glycosidase activity.