Mild oxidation of glucoamylases from Aspergillus niger (E.C.3.2.1.3.) with periodate, followed by incubation with adipic acid dihydrazide, covalently linked enzyme molecules via their glycosyl groups. Size exclusion chromatography demonstrated and electron microscopy confirmed the formation of tetramers and octamers. Heat inactivation studies in the range of 60 degrees to 80 degrees C indicated that, in contrast to a priori expectations, crosslinking via the carbohydrates decreased rather than increased thermostability. The covalently linked species, even the octamers, displayed similar activity as the native forms toward maltose and soluble starch, but activity toward raw starch was completely lost.