There were a few reports studying on the cell kinetics and migration of proliferating lymphocyte in the germinal center of palatine tonsil and most of them were performed by obtaining autoradiographys after exposing to a pulse ³H-thymidine. However, autoradiographic studies required several months to complete and the results were of limited value in studying the cell kinetics. Recently, it becomes also possible to detect replicating cells that have incorporated 5-Bromodeoxyuridine(BrdU), using immunohistochemical techniques with monoclonal antibodies against BrdU, and so possible to avoid time-comsuming autoradiographic procedures. We observed the cell kinetics and migration of the proliferating lymphocyte in the germinal center of palatine tonsil in the normal rabbit. BrdU(50mg/kg body weight) was administered intravenously to the rabbits. The rabbits were sacrified and tonsils were removed from 30 minutes to 5 day after injection respectively. The BrdU incorporated cells were detected by immunohistochemical method utilizing anti-BrdU antibody. The results were as follows : 1) Thirty minutes after BrdU injection, BrdU-labeled cells were concentrated in the basal part of the germinal center. 2) Two hours after BrdU injection, BrdU-labeled cells were concentrated from basal part to light zone of the germinal center. 3) Eighteen hours after BrdU injection, BrdU-labeled cells were concentrated at maximum in the germinal center and the crypt epithelium. 4) Three days after BrdU injection, BrdU-labeled cells were seen partially in the germinal center and crypt epithelium, but decreased than that of eighteen hours. 5) Five days after BrdU injection, BrdU-labeled cells were not observed in the germinal center and crypt epithelium. It is supposed that proliferating lymphocytes in germinal center of palatine tonsil maybe migrate from the basal part of germinal center to the crypt epithelium and the turnover of the proliferating lymphocyte may be within five days.