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], 3',4'-dihydroxyflavanone [4], 3-hydroxyflavone [2], flavone [5], 2'-hydroxydihydrochalcone [7], 2',4-dihydroxydihydrochalcone [6], 2',3,4-trihydroxydihydrochalcone [8], 2',5'-dihydroxydihydrochalcone [9], 4'-hydroxyflavan-4 alpha-ol [11], and 2'-hydroxydibenzoylmethane [10]. The isoflavanone metabolites were identified as isoflavone [15], 2-hydroxyisoflavanone [16], 4'-hydroxyisoflavanone [13], 6,4'-dihydroxyisoflavanone [17], and 3',4'-dihydroxyisoflavone [14]. 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.