Starch consists of of two main fractions, amylose and amylopectin. The amylose molecules are unbranched chains of glucose residues joined only through a-glucosidic 1,4 linkages, whereas the amylopectin is a highly branched molecule which contains, in addition to 1,4 linkages, a-glucosidic 1,6 linkages at the point of branching. Is used as a substrate for serum amylase (Street, H.V. and Close, J.R., Clin Chem Acta, 1, 256, 1956). The preparation is essentially free of amylopectin.