Publisher Summary This chapter discusses polyuronides. The uronic acids are aldehyde carbonic acid derivatives of the hexose sugars. The polyuronides are the corresponding polysaccharides in which n hexuronic acids are combined according to the principles of glycoside formation with the exclusion of (n − 1) molecules of water to form macromolecules containing many hexuronic acid residues. The proportion of these units in the polysaccharide may be small as in the case of some gums and exudates of plants and in various polysaccharides produced by microorganisms. Uronic acid units may account for about one-half of the building units of the polymer as in hyaluronic acid, which is composed of equal parts of D-glucuronic acid and N-acetyl-n-glucosamine. In addition to D-glucuronic acid, D-galacturonic acid, and D-mannuronic acid, some other uronic acids have been found to occur in polysaccharides: the L-iduronic acid in chondroitin sulfate B may be noted as such an example. The chapter describes hyaluronic acid and some other polysaccharides containing lower proportions of uronic acid units.