The kinetic changes of the number of antigen-specific B cell (ASC, sIg~+, Ig-non-secreting), preplasma cell (sIg~+, Ig-secreting) and plasma cell (sIg~-, Ig-secreting) in the spleens of inbred sibling Balb/c mice during the continuous OA immunization process were assayed, and their relationship to the corresponding spccific efficiency of the hybridoma formed was compared. The results show: the specific efficiency of hybridoma formation is parallel with the kinetic changes of the number of ASC, but not with the number of preplasma or plasma cells. So we suggest that the antigen activated B lymphocytes in proliferating state, but neither the antibody-secreting cells (i.e. preplasma cell and plasma, cell) nor small B lymphocytes are partners fused with the myeloma cells to yield functional hybridoma cells. The kinetic changes of the number of antigen-specific B cells (ASC, sIg ~ +, Ig-non-secreting), preplasma cells (sIg ~ +, Ig-secreting) the spleens of inbred sibling Balb / c mice during the continuous OA immunization process were assayed, and their relationship to the corresponding spccific efficiency of the hybridoma formed was compared. The results show: the specific efficiency of hybridoma formation is parallel with the kinetic changes of the number of ASC, but not with the number of preplasma or plasma cells. So we suggest that the antigen activated B lymphocytes in proliferating state, but neither the antibody-secreting cells (ie preplasma cells and plasma, cells) nor small B lymphocytes are partners fused with the myeloma cells to yield functional hybridoma cells.