YOSHIE, O. and ONO, Y. Frequencies of Specific Antibody-Producing Cells for Sheep Red Blood Cells and for Phosphorylcholine in Human Tonsillar B Lymphocytes Transformed by Epstein-Barr Virus. Tohoku J. exp. Med., 1982, 137 (3), 233-244-The frequencies of transformed B cells and of transformed specific antibody-producing cells in human tonsillar lymphocytes infected with Epstein-Barr virus (EBV) were determined by limiting dilution analyses. The latter was corrected by the former and the frequencies of specific antibody-producing cells in EBV-transformed B cell populations were obtained. The frequencies of specific B cells for sheep red blood cells were calculated to be one in 500 to 2, 000 EBV-transformed tonsillar B cells obtained from four donors, while those of specific B cells for a hapten, phosphorylcholine, were one in 700 to 5, 000. The method may be useful to define the repertoire of specificities in the human B cell populations.