The microbiological transformation of flavanone and isoflavanone was explored using a group of 80 microorganisms in the initial screening. Ten metabolites of flavanone were isolated and identified as 4'-hydroxyflavanone , 3',4'-dihydroxyflavanone , 3-hydroxyflavone , flavone , 2'-hydroxydihydrochalcone , 2',4-dihydroxydihydrochalcone , 2',3,4-trihydroxydihydrochalcone , 2',5'-dihydroxydihydrochalcone , 4'-hydroxyflavan-4 alpha-ol , and 2'-hydroxydibenzoylmethane . The isoflavanone metabolites were identified as isoflavone , 2-hydroxyisoflavanone , 4'-hydroxyisoflavanone , 6,4'-dihydroxyisoflavanone , and 3',4'-dihydroxyisoflavone . The structures of the metabolites were established using spectroscopic techniques including ir, ms, uv, 1H-nmr, and 13C-nmr spectroscopy. Production of 4'-hydroxyflavanone, 3',4'-dihydroxyflavanone, and 2',4-dihydroxydihydrochalcone by 13 microorganisms was assayed using reversed-phase hplc.