Eubacterium ramulus, a flavonoid-degrading anaerobic bacterium from the human gastrointestinal tract, was tested for its ability to transform the isoflavonoids genistein-7-O-glucoside (genistin), genistein and daidzein. Genistein was completely degraded by E. ramulus via 6'-hydroxy-O-desmethylangolensin to 2-(4-hydroxyphenyl)-propionic acid. Dihydrogenistein was neither observed as an intermediate in this transformation nor converted itself by growing cells or cell-free extracts of E. ramulus. Genistein-7-O-glucoside was partially transformed by way of genistein to the product 2-(4-hydroxyphenyl)-propionic acid. Daidzein was in part degraded to O-desmethylangolensin, the corresponding metabolite to 6'-hydroxy-O-desmethylangolensin. The hydroxyl group in position 6' of O-desmethylangolensin is crucial for further degradation.