Chitin, a linear polysaccharide composed of (134)-linked 2-acetamido-2-deoxy-b-D-glucopyranose (GlcNAc) residues, and chitosan, the fully or partially N-acetylated, water-soluble derivative of chitin composed of (134)-linked GlcNAc and 2-amino-2- deoxy-b-D-glucopyranose (GlcN), have been proposed as elicitors of defense reactions in higher plants.