Four spaced injections of Newcastle disease virus were given to laying fowls. A state of hyperimmunity was reached at the 42nd day and was maintained up to the 91st day when haemagglutination inhibition antibody titre started to fall. Haemagglutination inhibition antibody produced by the hen could be detected both in egg yolks and chicks although to a lower titre than in the serum of the hen. Fuctuation of antibody transmitted by the individual hens was observed.