The Bursa Fabricus and the thymus so similar that both of them are called central immune organs from the functional view point or lymphoepithelial organs from the morphological view point. Their reponses to various injuries are also similar. Kim and colleagues studied the origin of plasmocytes under various experimental conditions and confirmed that a strong transient plasmocytogensis appeared in the thymus of rats after whole body X-ray radiation. So, the author attempted to confirm whether plasmocytogenesis could be induced in Bursa Fabricus of chickens by whole body radiation or not. As a result, the author confirmed a strong transient plasmocytogenesis in the follicle of Bursa Fabricus 24 hours after 400 R-whole body radiation. In the normal follicle of Bursa Fabricus, there is no plasmocytogensis. However, massive destruction of small lymphocytes took place in the follicle after X-ray radiation, followed by a transient plasmocytogenesis, which preceded regeneration of small lymphocytes.