To isolate the pathogenic agent from the patients of infectious hepatitis in Okayama Prefecture, the author inoculated patient materials into various sorts of laboratory animals. The results are briefly summarized as follows: 1) By inoculation of the patient blood, the feces and the liver emulsion into the embryonated hen's egg, a few strains of virus could be isolated. The inoculation by the chorio-allantoic route gave the most excellent result, and the serial passge could be well carried out by the infected chick-embryo. 2) The hamster did not succumb to inoculation of the virus habituated to the chick-embryo. In the liver, however, high degre of degeneration and round cell infiltration around Glisson's sheath were observed, which could be regareded as the mark of infection. The reinfection from the hamster to the chick-embryo could be also well established.