We established an anti-thyroglobulin antibody-producing cell line using the peripheral lymphocytes from a patient with chronic thyroiditis. The method was based on preselection by "panning", transformation by EB virus and twice clonings by "limiting dilution". The cells of the cloned cell line (Yo3CTX10) had neither E-receptor nor IgG X Fc-receptor but had C3-receptor as shown by rosetting. We could not detect surface immunoglobulin, but we could detect cytoplasmic immunoglobulin (IgG lambda) with FITC-stainings. This cell line has continuously secreted anti-thyroglobulin antibody for 8 months, which was IgG lambda as shown by immunoelectrophoresis and solid phase radioimmunoassay. The pattern obtained using the purified antibody showed two sharp bands (H, L-chains) in SDS polyacrylamide gel electrophoresis, but it showed six sharp bands in isoelectric focusing electrophoresis. Thus we could establish an oligoclonal cell line producing IgG lambda anti-thyroglobulin antibody.