A novel extracellular amylase of alkalophilic Bacillus sp. IMD 370 was purified to homogeneity and displayed maxima for activity at pH 10.0 and 40 degrees C. It had an isoelectric point of 4.9 and a relative molecular mass of 159,000 as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and was inhibited (47%) by ethylenediaminetetraacetic acid (1 mM). The alpha-amylase of Bacillus sp. IMD 370 was quite distinct by virtue of its mechanism of action and its inability to fit into the conventional classification scheme of amylolytic enzymes. It had a mode of action intermediate between an endo-acting enzyme, alpha-amylase, and a typical exo-acting enzyme, amyloglucosidase. The sugars produced on hydrolysis of starch had the alpha-configuration, but no oligosaccharide higher than maltotetraose was obtained at any stage during starch hydrolysis.