The known endemic regions of schistosomiasis japonica include five relatively small areas in the Japanese home islands, a vast territory in the Yangtze valley of Central China and several watersheds in South China, a small focus in Formosa, portions of the islands of Mindoro, Leyte, Samar, and Mindinao in the Philippines, and one small area in northern Celebes. In Japan and along the south coast of China the molluscan intermediate host is Onconmelania (Katayama) nosophora; in the Yangtze valley it is O. hupensis; in Formosa, O. formosana, and in the Philippines, O. quadrasi. The intermediate host in Celebes has not been identified.