The rearrangement of bcl-2 gene was studied in 56 Japanese B cell lymphoma cases to investigate the contribution of bcl-2 gene to lymphomagenesis in Japan. Ten out of 56 cases showed bcl-2 gene rearrangement; it was detected in only 5 out of 16 follicular lymphoma cases (31%) and in 5 out of 40 diffuse B cell lymphoma cases (13%). The incidence of bcl-2 gene involvement in Japanese follicular lymphomas was lower than those reported in the United States. This might contribute to the lower incidence of follicular lymphoma cases in Japan. Novel recombination between bcl-2 and Ig kappa genes at the 5' region of bcl-2 and J kappa 4 segment was observed in one follicular lymphoma case, suggesting that bcl-2 gene is transcriptionally activated by Ig kappa enhancer. It was also suggested that this case had originated from a more differentiated B cell than most follicular lymphomas with bcl-2-Ig H recombination.