The authors examined 4, 245 patients received in the Kure National Hospital and 318 samples of preserved blood were determined as Australia antigen in relation to diagnosis of hepatitis from the beginning of February to September in 1970. A positive reaction to Australia antigen was observed in 78 of 4, 245 cases and three out of 318 samples of preserved blood. Nine of 78 cases were diagnosed and confirmed as acute hepatitis. Two of 9 subjects who were diagnosed to be acute hepatitis, had past records of blood transfusion relating to hepatitis. In another 30 of 78 subjects, the liver function tests were made and found to be entirely normal and the history of blood transfusion was noted in 4 of these 30. The remaining 30 cases were diagnosed and proved to contract chronic hepatitis and recrudescence of serum hepatitis. In seven cases of acute hepatitis without any record of blood transfusion in which Australia antigen were determined in serum, Australia antigen could be observed only in one to three weeks from the initial examination. Furthermore, it is pointed out, from the observation of the severe stage of acute hepatitis, that the patients who showed a positive reaction to Australia antigen seemed to have had a more prolonged course than the negative. Studying the residential distribution of Australia antigen positive patients, it is indicated that the results obtained were very similar to those of the patients of bacillary dysentery and its carriers, with exception of the patient isolated in the area with the complete sewerage.