Immobilized enzymes are provided in which the enzyme is covalently linked by a disulphide group-containing bridge to on inorganic or organic support carrier. Immobilizing by this method enables spent immobilized enzyme to be readily regenerated by reduction under mild conditions of the disulphide bridge to provide the carrier with mercaptan groups, and adding fresh enzyme to the carrier. The immobilization method is applicable to a wide variety of enzymes using the same chemical coupling reagents. The method is especially useful for immobilizing expensive enzymes such as glucose isomerase.