Employing the chick-embryo method by Murakami et al., the auhtor succeeded to isolate the similar pathogenic agents by the chick-embryo and mouse from the patients of infectious hepatitis in Okayama prefecture. The results were as follows: 1) The natures of the pathogenic agents isolated by the author were nearly the same as those of the one reported by Murakami et al., and this fact proved that the method by Murakami et al. was of practical use for the isolation of the hepatitis virus. 2) The virus habituated by the successive cultivation in embryonated hens, eggs could cause the infection in the mouse. 3) The direct inoculation of the materials of the hepatitis patients into the mouse often failed in the isolation of the virus. It was proved, however, that the isolation was successful even withoul the successive cultivation in embryonated eggs if the used materials and the inoculation method were proper. The natures of the virus isolated by the mouse seemed to be the same as those of the one isolated by the chick-embryo. 4) The isolation of the virus by the direct inoculation of the liverpunctur material into mice or embryonated eggs succeeded only in one case. Theis method was considered, however, to be a useful method for the clinical diagnosis of chronic hepatitis in future.