Glycosaminoglycans are linear, sulfated polysaccharides that are found in virtually all animal tissues. With the exception of hyaluronic acid, glycosaminoglycans are biosynthesized as proteoglycans in which one or more glycosaminoglycan chains are attached to a core protein (1). Chondroitin and dermatan sulfates are comprised of alternating 1→3, 1→4 linked N-acetyl-d-galactosamine and hexuronic acid (either d-glucuronic or l-iduronic acid) residues. These saccharide residues can be O-sulfonated at various positions on both sugar residues. Heparin and heparan sulfate are structurally related and are comprised of a hexuronic acid residue (either l-iduronic or d-glucuronic acid) 1→4 linked to a D-glucosamine (either N-sulfo or N-acetyl-d-glucosamine) residue. Both saccharide residues can be O-sulfonated at a variety of different positions, making these glycosaminoglycans structurally complex. Hyaluronic acid contains a simple repeating structure of 1→3, 1→4 linked N-acetyl-d-glucosamine and d-glucuronic acid residues. Hyaluronic acid is an unusual glycosaminoglycan as it is not sulfonated and can have a very high molecular weight, up to 2 � 106 Da compared to 1–3 � 105 for the other glycosaminoglycans. Keratan sulfate is a glycosaminoglycan that contains no uronic acid and is comprised of a repeating 1→3, 1→4 linked, O-sulfonated N-acetyl-d-glu-cosamine and d-galactose residues.