A high molecular weight elicitor (> 70 kDa) from spore germination fluid of a pea pathogen, Mycosphaerella pinodes, has a partial structure of beta-D-Glc-(1-->6)-alpha-D-Man-(1-->6)-D-Man, which is O-glycosidically attached to serine in the protein moiety. To elucidate the minimum structure for the elicitor activity to pea plants, the effects of nine glycopeptides including beta-D-Glc-(1-->6)-alpha-D-Man-(1-->6)-D-Man-O-Ser (No. 1) to [beta-D-Glc-(1-->6)-alpha-D-Man-(1-->6)-D-Man]3-O-Ser3-Pro3 (No. 9) on the infection by M. pinodes, superoxide generation and ATPase activity were measured. The glycopeptides [beta-D-Glc-(1-->6)-alpha-D-Man-(1-->6)-D-Man]-O-Ser2-Pro2 (No. 3) to No. 9 induced rejection reaction of pea tissue against M. pinodes. The glycopeptides No. 3 to No. 9 also induced superoxide generation on uninjured pea leaves. Moreover, the glycopeptides No. 3 to No. 9 induced in vitro the activation of cell wall-bound ATPase and superoxide generation system in the protein fraction solubilized from pea cell wall. The results indicate that the synthetic glycopeptides, No. 3 to No. 9, are available to analyze the signal transduction cascade leading to defense responses and the receptor for the elicitor.