The ability of chitin oligomers and chitosan to act as elicitors of the defense system of cucumber and bean plants was examined. Induction of chitinase, peroxidase, beta-1,3-glucanase, and chitosanase was examined by spraying the plant leaves with chitin and chitosan oligomers or with chitosan polymers having a 5 or 30% degree of acetylation (DA). Chitin oligomers and chitosan induced the activity of these enzymes in cucumber and bean plants; chitin oligomers induced high peroxidase activity in cucumber, beta-1,3-glucanase activity in bean, and chitosanase activity in both cucumber and bean plants. Chitosan significantly induced the activities of chitosanase and chitinase in both cucumber and bean plants. Chitosan oligomers did not induce any enzymatic activity in cucumber or bean plants. Increasing the DA of chitosan from 5 to 30% appreciably increased the elicitation of chitinase, peroxidase, and beta-1,3-glucanase activities in cucumber and bean plants. It is suggested that the elicitation of the 2-amino-2-deoxy-beta-D-glucopyranose oligomers or polymers is controlled by the DA.