Examination was made of the urinary and biliary excretion of the metabolites of genistein and genistein, the major components of Glycine and Sophora genus in rats. The urine of rats administered genistein orally contained eight metabolites. Three of these metabolites, genistein 4'-O-sulfate (M-1), genistein 7-O-beta-D-glucuronide (M-3), genistein 4'-O-sulfate 7-O-beta-D-glucuronide (M-6), were identified from spectroscopic and chemical data. The bile of rats administered genistein orally contained M-2, M-3 and M-6. M-6, a major biliary metabolite, was isolated and identified from spectroscopic and chemical data. The urine or bile of rats treated with genistein, the glycoside of genistein, contained M-1-M-8 or M-2, M-3, M-6 in the above metabolites. These findings suggest that genistein is absorbed as genistein after hydrolysis in the gastrointestinal tract. The total cumulative amounts of the two metabolites and genistein excreted in the urine during 48h, or of M-6 excreted in the bile during 36h following the oral administration of genistein, were approximately 5.7% or 16.0% of the doses administered, respectively. The result show that M-1, M-3 and M-6, having a free hydroxyl, glucuronide- or sulfate-conjugated hydroxyls at the C-7 or C-4' position, are excreted in the urine and bile as parts of the metabolites of genistein.