beta-Glucosidase immobilized on a reversibly soluble-insoluble polymer, G-AS, was utilized for the hydrolysis of phloridzin. The solubility of the immobilized enzyme was dependent on pH and temperature of the solution : its responsive ranges was between pH 4.0 and 5.0 at 50 degrees C and between pH 3.5 and 4.5 at 4 degrees C. Soluble G-AS had a higher specific activity toward phloridzin than that of the conventional enzyme immobilized on a water-insoluble carrier. For the hydrolysis of phloridzin at a concentration of 5 g/l (the reaction produces a water-insoluble product from a water-soluble substrate), G-AS was used repeatedly and was easily separated by centrifugation from the reaction mixture containing a water-insoluble product. In addition, for the hydrolysis of phloridzin at a concentration of 50 g/l (the reaction produces a water-insoluble product from a slightly water-soluble substrate), G-AS was also used repeatedly and was separated for reuse from the mixture of unreacted phloridzin, glucose, and phloretin. The reaction method using such a reversibly soluble-insoluble enzyme in a heterogeneous reaction with a water-insoluble product is a potential procedure for repeatedly utilizing the enzyme and separating the water-insoluble product from the suspended mixture.