In order to assay one Iot of the potency of tuberculin for intradermic use, four guinea pigs sensitized with heat killed M. tuberculosis were used by the method originally of the Agricalture Research Service Center (A. R. S. ) and Bureau of Animal Industry (B. A. I. ) in the United States of America in which guinea pigs were used on 21st day after sensitization, There is doubt whether the guinea pigs are sensitized or not. Therefore, this study has taken the method of Middle Brook-Dubos hemagglutination test, and observed the humoral hemagglutinating antibody in the blood. The results obtained are as follows. 1. The maximum titer of hemagglutinating antibody was demonstrated 30days after sensitizing the guinea pigs with kilIed tubercle bacilli. The maximum titer was continued for a period of 45 days and thereafter declined gradually. 2. The swelling and redness of the region of the sensitized guinea pigs was shown to be reached to the maximum size within 24 hours after intradermal ineculation with HCSM tuberculin and gradually reduced 96 hours after inoculation. The swelling and redness could not be detected by macro-observation after 14 days.