4-Nitrophenyl 2-acetamido-3-O-[2-O-a-L-fucopyranosyl-b-D-galactopyranosyl)-2-deoxyb-D-galactopyranoside is a water soluble, fluorescent probe that can be used for detecting the presence of ?-(1?4) -linked galactosaminoglycans. The dye is a substrate for enzymes such as ?–mannosidase, ?–glucuronidase and ?–galactosidase. The dye is also an excellent ligand for lectins such as concanavalin A and wheat germ agglutinin.