The vicissitude of the heterophile antibody was observed on the inhabitants at the epidemic districts of epidemic hepatitis in Okayama prefecture, especially the correlation between the heterophile antibody and the epidemic transition of epidemic hepatitis were observed and several noteworthy significance of the heterophile antibody on the prevalence of epidemic hepatitis was obtained. 1. The rise of the heterophile antibody titer at the epidemic time of epidemic hepatitis was not seen any difference on the sex distinction and the age distinction, and the difference of the heterophile antibody production was not seen by the sex distinction or the age distinction. 2. Remarkable difference were observed on the appeared frequency of the heterophile antibody in the epidemic time and non-epidemic time of epidemic hepatitis, and it was certified that there was the close relation between the appearance of the heterophile antibody and the epidmy of epidemic hepatitis since the heterophile antibody showed the high positive rate in the epidemic time. 3. The positive rate of the heterophile antibody was high in the inhabitants of the epidemic district before and after the prevalence of epidemic hepatitis and the cases with the past history of hepatitis, and the heterophile antibody (over 40 times of agglutination titer was identified for a considerable long time in the above cases). 4. No coreelation between the rise of the heterophile antibody and the epidemic state of epidemic hepatitis of the form of epidemic hepatitis was not certified.