As a trial toward the elimination of Japanese encephalitis virus in natural surroundings, pigs were inoculated with inactivated Japanese encephalitis vaccine supplemented with complete Freund's adjuvant three times at one week and five weeks intervals. Effect of adjuvant supplement on antibody response and prevention of viremia caused by natural infection were investigated. In addition to this, inoculation of live attenuated vaccine with simultaneous administration of adjuvant in another site was conducted to examine the antibody response in pigs.The results of this study are summarized as follows.1. In the group of pigs inoculated with vaccine containing adjuvant, titers of hemagglutination inhibiting and neutralizing antibodies were higher than those of pigs inoculated with vaccine alone and their high titers persisted.2. With respect to natural infection of pigs, on August 22, when the pigs were thought to have been infected, the rise in antibody titer was observed. And the antibodies in pigs received vaccine with or without adjuvant were proved to be all 2-ME resistant type, wherease the antibodies in control group were 2-ME sensitive antibody.3. Viremia was detected in the blood of pigs naturally infected, but it was not demonstrated in pigs received vaccine with or without adjuvant. The virus of pig blood which was isolated after a few passages in suckling mouse brain was sup posed to be JaGAr 01 type strain from optimum hydrogen ion concentration of its hemagglutination reaction.4. Effect of vaccination on antibody response of pigs having maternal antibody was not recognized.5. In the group of pigs inoculated with live attenuated vaccine and adjuvant, average titer of hemagglutination inhibiting antibody was higher than those in pigs inoculated with vaccine alone and their titer persisted.