Vaccination of broiler breeder parents with live infectious bursal disease (IBD) vaccine by the oral route resulted in higher and more persistent quantitative gel diffusion precipitins than vaccination by intramuscular injection. All the progeny of the orally vaccinated parents had maternally derived IBD antibody (MDA) at hatching while MDA was detected in only 35 per cent of the progeny of the intramuscularly vaccinated parents. This MDA had disappeared completely at 14 and eight days respectively. Susceptibility to IBD challenge began at eight days in the first group and at one day old in the second. The age of 100 per cent susceptibility occurred at 19 and 11 days in the respective groups.