To evaluate the role of B-1 cells and polyreactive autoantibodies in the development of adult immune repertoire, it is necessary to assess their immunoglobulin heavy chain variable-gene usage. We thus screened 28 independently derived human polyreactive MAbs from fetal and adult splenic B lymphocytes for their VH-region usage. We demonstrate that the polyreactivity of the IgM antibodies secreted by B-1 cells is not the result of the expression of particular variable region gene families. All six VH families are represented roughly in proportion to their estimated family size. Furthermore, the representation of the six families appears similar in polyreactive MAbs derived from fetal or adult lymphocytes.