Induction of resistance was studied in rice plant-Xanthomonas oryzae system by inoculating leaves primarily with incompatible strain or nonpathogen and challenging with a compatible strain. Lesion enlargement was markedly inhibited by the preliminary inoculation with incompatible strains of X. oryzae, but not with compatible strains. Inhibition was higher in the region located closer to the site of primary inoculation and was significant even in the tissue located 5cm apart from the site of primary interaction. Inhibition was highest when challenge inoculation was made 3 days after inducer inoculation and was remained effective until 9 days after preinoculation. Among 14 species of nonpathogenic bacteria tested, P. phaseolicola, X. citri, P. marginalis, and C. michiganense were highest in their ability to induce resistance, followed by P. solanacearum, X. campestris, P. lachrymans, E. carotovora, and X. phaseoli. C. sepedonicum, P. tabaci and A. tumefaciens were able to induce a weak resistance and X. pruni and X. phaseoli f. sp. sojense did not induce any resistance. These nonpathogenic bacteria, however, did not induce detectable resistance in the region located more than 3cm from the site of inducing interaction and when challenge inoculation was made 6 or more days after the inducer inoculation. Among saprophytes tested, 2 contaminants isolated from culture plates of X. oryzae produced a clear inhibition zone on plating and were also capable of inducing resistance, but 3 others isolated from healthy rice leaves did not induce resistance. Preliminary results suggested that neither nutritional competition nor production of antibacterial substance by the primary bacteria seemed responsible for this type of induced resistance, at least not with X. citri and P. tabaci.