A study was carried out under a collaborative research between MAFF, Japan and IRRI, Philippines, to establish international differentials for identifying of bacterial blight by developing near-isogenic lines with single genes for resistance. The resistance to bacterial blight of two resistant cultivars Zenith and Cempo Selak was analyzed using Japanese and Philippine races of bacterial blight at two locations; TARC in Japan and IRRI in the Philippines. Rice cultivar Zenith had been identified to possess Xa-6 gene, whereas the genetic composition of Cempo Selak, one of IRRI differentials was unknown. The reaction of these cultivars to Japanese and Philippine races was similar to the reaction of Chugoku 45 and Java 14 in our preliminary tests. We carried out genetic analysis of these two cultivars for resistance to bacterial blight and carried out allelic tests with Xa-6 present In Chugoku 45 and Java 14. The reaction of F₁, F₂, and F₃ progenies from the crosses of IR24 with Zenith and Cempo Selak showed that these two cultivars also have Xa-3 for resistance and the gene symbol Xa-6 assigned to the dominant gene of Zenith is redundant.