Starch is a plant reserve polysaccharide, an end product of carbon fixation by photosynthesis, in which D-glucosyl units are linked predominantly by α-(1,4) bonds. Starch is, basically, a polymer of α-D-glucose. At least two polymers can be distinguished: amylose, which is essentially linear, and amylopectin, which is highly branched. Purification of the starch synthase and branching enzymes in large amounts and to a large specific activity has proven to be difficult. Partly for this reason it has not been possible so far to find out how the enzymes interact to produce the two carbohydrates, amylose and amylopectin, that form the starch granule. Amylases can interfere with the measurement of branching enzyme, and for this reason suitable controls and blanks are essential. The agricultural industry is interested in increasing starch content and in tailoring the starch properties genetically to suit the diverse uses that, at present, require chemical modification of starch or the use of expensive imported natural starches.