In this report, the problem of infectious spectrum of hepatitis virus was studied by observing the establishment of infection and passage in various kinds of animals. The virus isolated from the hepatitis patients in Okayama Prefecture was used throughout this work, and the establishment of infection and passage was judged by the pathological appearances, of tissues. particularly of liver as the center, of inoculated animals. The results were as follows: 1) In mouse, embryonated egg and young hamster, the infection and passage of hepatitis virus were established. 2) In rat, guinea-pig, young dog and young cat, the establishment of infection could not be proved with certainty. 3) Among the used strains of virus, some difference was observed, which was probably originated from the difference of conditions at the isolation and passage of them. It was not conceivable, however, that remarkable difference of pathogenicity was present among them. 4) Putting together the aspects of infection, pathological figures and general natures of virus from the results of animal tests, the virus used in the present work is very simillar to the one reported by Havens, Maccallum and Wildführ.