A murine monoclonal antibody HAb27 specific for human hepatocarcinoma has been developed for radioimmunolocalization in animal models. The isotype of this antibody was IgG1, k. In the present study, we used a set of oligonucleotide primers to amplify the cDNA of mouse immunoglobulin heavy and light chain variable region genes by the polymerase chain reaction. Sequence analysis of the heavy variable region indicated that the V_H region was highly homologous to the plasmacytoma cell line MOPC21 gene, and closely related to germline genes of the V_HIII family. The J_H region was encoded by the J_H3 gene. For the light chain, the V_K segment of the antibody showed the highest homology to the germline V_KOxl gene, and the J_K: region was J_K5.