A new B-cell line (ONHL-1) was established from non-Hodgkin's lymphoma. ONHL-1 was free from Epstein-Barr virus nuclear antigen and expressed CD20, CD24, and slg (mu, delta, gamma and kappa), thus being equivalent to the mature B-cell stage. Chromosome analysis revealed a markedly abnormal pattern including 14q+ and 6q-. In accordance with the positive expression of surface kappa light chains, one of the kappa genes was found to be rearranged. However, rearrangement of the lambda locus was also detected, contrary to the supposed hierarchy for the rearrangement of the light-chain genes. Further, the rearranged fragments of the JH, C lambda, and bcl-2 genes were of the same size in the EcoRI and HindIII digests on the same filter. This may suggest that the bcl-2 gene is juxtaposed with the JH and C lambda locus. The proliferation of ONHL-I was inhibited by adding Staphylococcus aureus Cowan 1 or 12-O-tetradecanoyl-phorbol-13-acetate. During this growth inhibition, the expression of c-myc decreased, while that of bcl-2 mRNA remained steady. This result suggests that not the bcl-2 gene but other oncogenes, such as c-myc, play a key role in the proliferation of ONHL-1. This agrees with the hypothesis that the bcl-2 gene is not concerned with aggressive proliferation but with cell survival. This new cell line will therefore be of value in studying the differentiation and tumorigenesis of B cells.