Recent studies identified two major catabolites of a mixture of silybins A and B. These catabolites have the molecular formulas C24H20O10 and C24H22O10: the first corresponds to demethylation of the methoxy group on the D-ring of silybin B; and the second corresponds to the combination of this demethylation with reduction of the ether bridge on the D-ring of silybin A between C11 and C12a to form methylene. These results are consistent with our experiment.