Experiments described in this paper confirm the view that β-malt amylase selectively hydrolyzes one portion of the starch substance; this fraction (approximately 60% of the starch substance) is transformed into maltose and there remains a residual non-reducing fraction (erythrogranulose) which retains the property of iodine coloration. With regard to α-malt amylase, several lines of evidence indicate that this enzyme does not exert a selective action upon the erythrogranulose fraction, as is suggested in a current theory of starch constitution, but that it induces the breakdown of both fractions. In this case the reducing products do not consist exclusively of maltose.