Under optimum conditions (pH 5, 75 degrees C, and 0.2 U purified enzyme ml(-1)), 4 mg ginsenoside Rd was produced from 5 mg reagent-grade ginsenoside Rb(1) in 5 ml after 30 min by beta-glucosidase from Thermus caldophilus GK24. Using a ginseng root extract containing 1 mg ginsenoside Rb(1) ml(-1) and 3.2 mg additional ginsenosides ml(-1), 1.23 mg ginsenoside Rd ml(-1) was produced after 18 h; the concentrations of ginsenosides Rb(1), Rb(2), and Rc used for ginsenoside Rd production were 0.77, 0.17, and 0.19 mg ml(-1), respectively.