We have previously shown that long-term in vitro proliferating fetal liver pre-B cell lines derived from autoimmune-prone (NZB x NZW)F1 (BW) mice, but not normal (B6 x DBA2)F1 mice, can differentiate in severe combined immunodeficient (SCID) mice to produce elevated levels of serum immunoglobulin (Ig) M and IgG, and high titers of antinuclear antibodies The contribution of parental NZB and NZW strains to B cell abnormalities of BW hybrid mice was investigated here by preparing pre- B cells and transferring them into immunodeficient SCID- and RAG-2- targeted mice. We show that transfer of NZB pre-B cells led to a marked IgM hypergammaglobulinemia and to the production of limited amounts of IgG2a. On the other hand, the transfer of NZW pre-B cell lines led to moderately elevated IgM levels and marked hypergammaglobulinemia of IgG2a. High IgM and low IgG anti-DNA titers are found in the recipients of NZB pre-B cells, whereas those receiving NZW pre-B cells contained lower levels of IgM and high titers of IgG anti-DNA. In marked contrast, essentially identical titers of antibodies directed against a non-self-antigen, DNP, are found in all group of pre-B cell recipients. Thus, B-lineage cells of both NZB and NZW parental strains manifest abnormalities associated with the development of this lupus-like disease. Therefore, the present study strongly suggests a complex inheritance of B cell abnormalities in autoimmune-prone (NZB x NZW)F1 mice and emphasizes the critical importance of intrinsic B cell defects in the development of murine systemic lupus erythematosus.