Zymograms of the cultural supernatant of Alcaligenes sp. showed three bands, the major one being G4A-1 and the minor two, G4A-2 and G4A-3. Based on the electrophoretic homogeneity of the purified three bands and the enzymatic activities identified by a thin layer chromatography of the soluble starch hydrolysates, all the three bands were confirmed to be maltotetraose-forming amylase but in multiple forms. Neither glycosidase nor protease activities could be detected in the culture (only very weak protease activities were observed at 48 hours after cultivation), which indicate that the two enzymes were not involved in the amylase multiple-form formation. Only the relative amount of the two minor bands (but not the multiple-form pattern) was changed when the initial pH of the medium varied from 6.5-8.5. An addition of 0.3% glucose raised the yield of G4A-2 and G4A-3.