1 Serum samples were cc&ted for HI test aft inccu]ation with aluminum hyd-roxiel atorkei inactivated Newcastle vaccine. The HI titer was keginning to rise at 2nd week, reaching to the uiincGt at 3rd or 4th week, and gradual disaparance at 6th week aft vaccination, The HI titier a]mcGt lcGt and did not differ from no vaccination at 12th week aft vaccination,.
2.Above chickens that HI titer had lost were challengal with virulent virus at 16th week aft vaccination. As result except that two chickens of no HI titer and four chickens of less Hltiterweredied, theothers oouldstandagainstvims challengeand?3% goation were found It immunity values seemed to ke aral]el with appearing HI titer to the utmost.
3. In order to understand the differ disappearing HI titer chickens alt Vacci-nation as result the neutalizing value of disappearing HI titer chickens was more than-log 1.3.
4.The maintuble pericd of neuta lizing values was apxenily longer than HI titer.