Lactobacillus delbrueckii subsp. delbrueckii KCTC 1047, grown in deMan, Rogosa and Sharpe (MRS) or soymilk media, completely hydrolyzed the isoflavone glucosides, genistin and daidzin at 50 mug ml(-1), into their respective aglycones, genistein and daidzein within 30 min. Other lactic acid bacteria did not produce beta-glucosidase, the enzyme responsible for the hydrolysis of isoflavone glucosides, when cultured in MRS medium. Glucoside-hydrolyzing activity was induced in some lactic acid bacteria when cultured in soymilk medium. These strains hydrolyzed 70-80% of genistin into genistein and 25-40% of daidzin into daidzein.