Comparative studies of the gross yields of unfractionated water-soluble gum-like materials from a number of cereals indicate that barley is probably the best source of laevorotatory glucosan and rye the best source of pentosan; wheat occupies an intermediate position, but oats and maize are poor sources of pentosan. In the case of some raw materials, and of adjuncts whose manufacture has involved heat or mechanical treatment, the gum-like materials are strongly contaminated with water-soluble polysaccharides of high dextrorotation, these contaminants probably representing products derived from starch. Extracts of rice grits and of flaked maize have low viscosities and the high yield from the latter is largely contaminated with dextrorotatory glucosan; a smaller yield from barley flakes is still heavily contaminated with dextrorotatory material, but the viscosity of solutions of this impure barley gum is moderately high, a fact of considerable practical importance. An examination of fractionated wheat grain (bran, parings, flour, germ) indicates that the endosperm is the principal source of the gum. An attempt to establish a similar finding for barley (with fractions separated by pearling) failed, owing to solubilization of starchy material by the abrasive treatment; it was, however, shown that no substantial amount of gum is obtained from barley husk.