Prophylactic treatments, including inoculations with γ-globulin derived from human serum and placenta, were taken to the epidemic of infectious hapatitis at kagato-cho, Wake-gum, Okayama Prefecture. After these treatments, observing the emergence of new patients of hepatitis for full one year, following results were obtained. 1) New patients emerged not only in the contrast group but inoculated one. Of the three group, inoculated with human serum γ-globulin, inocnlated with human placental γ-globulin and contrast group, percentage of contraction is higher the inoculated group with human sernm γ-globtlin than others. 2) By the results of the mass examination, two groups were divided, the one included inapparent and latent infections, and the other was healthy cases. Observing the emergence of new patients in the group of healthy cases, percentage of emergence of the inoculated group with human serum and placental r-globulin was apparently lower than the contrast group. 3) From the facts above mentioned, it has been supposed that the inoculations with γ-globulin derived from human serum and placenta proved to have sufficient effect for non infected, but on the contrary little effect for infected before. 4) More than nine months after the inoculations, no prophylactic effect was supposed using inoculations with human serum γ-globulin for infectious hepatitis.