Since August 1951 to Feb. 1953, there was a great epidemic of serious infectious hepatitis over the area including Toyota, Onoda, Kama villages in Akaiwa County, as well as Kumayama village in wake County; observing its state, the following results were obtained. 1. Death toll has amounted to 13, out of 93 patients: its mortality rate, 13.98%; in number of the patients, Kama at the top, next, Toyoda, Onoda and Kumayama village, in literal order. 2. The epidemic took the direction, from the south extending to the north in a slow march, taking a hamlet as unit, showed a lack of specific seasonal occurence. 3. As to age, it has ranged roughly from 10 to 60, amid which 21-30 figured out as top years; below 10, only 4 cases; above 70, 5 cases. As to sex, almost similar in number. 4. As to profession, principally, farming people; as one can suppose from its locality. In making investigations into the cause of disease. certain consideration must be taken on the great responsibility imposed on farmers' wives. 5. The infection for this disease was classified as village infection or familiary infection; among 22 cases (23.4% of total patients) of familary infection, there were 4 families, each yielding even 3 sickened members; 5 families whose two members taken infection; in total, amnunted to 9 families. Among these tribal infection, report has been submitted about 1 family whose infection tract was clearly traced, as well as a family in which, if man did not expose certain inapparent infections, all cases have proved utterly whimsical. 6. The incubation period for this disease may probably be estimated to be about 24-27 days, if it may be supposed from these infectious state, and would be considered perorale infection.