Several specific monoclonal antibodies for B, T and natural killer (NK) cell were used to investigate the B cell localization and the expression of their phe- notype in lymphoid nodules on frozen and paraffin sections of human tonsil and lymph node by means of an immunocytochemical ABC technic. The results indi- cate that monoclonal antibodies reactive with germinal centers in tonsil and ly- mph node gave a simlar results and the results indicate that transformation and germination of germinal center cells involve phenotype changs but except T-200. For example, in the lower zone of germinal center, the lymphoblasts are weakly stained for IgM andLN-2 antibodies, but not for OKB-2 and BA-1, while in th upper zone the centrocytes are intense staining for IgM, LN-2, OKB-2 and BA-1 antibodies arelight or moderate staining separately Further charaterization of B cells in upperzone is frenquently observed clcavages on their nuclear memb- rane. In the mantle zone, the lymphocytes are strongly reacted with OKB-2 and BA-1, middle staining for LN-2 and light staining for sIgM. Plasma cell is only reactive with T-200 and IgM antibodies.