Forty pathogen free newzealand rabbits were used in this study. They were divided into 3 groups: the first group consisted of 24 infected intravenously with IBR virus. The second of 10 infected intranasally and the third of 6 as uninoculated control. The intravenous route proved to be the best one for studying the pathogenesis of IBR virus infection in rabbits. The virus affects
various organs with intranuclear inclusion bodies as well as endotheliosis. Moreover there is both humoral as well as cell-mediated immune responses as detected by Serum neutralization test (SNT) and leukocytic migration inhibitory factor (MIF) respectively.