The precursor frequency for anti-DNA antibody producing cells and the affinity of antibodies secreted by these cells in both immature prereceptor B cell populations and mature B cell populations were compared between 8-week-old C57BL/6 female mice and 9-month-old B/WF1 female mice by producing a large collection of IgM secreting hybridomas from LPS-stimulated B cells. The data indicate that precursor cells for high affinity anti-DNA antibody are eliminated as they mature in C57BL/6 mice, while a sizable number of such clones are present in mature splenic B cells of aged B/WF1 mice. These results suggest that the emergence of precursors for high affinity anti-DNA producing cells in mature B cell population is an important factor in the pathogenesis of SLE.