B cells that make polyreactive antibodies (PAB+ cells) express polyreactive Ig receptors on their surface and can bind a variety of different antigens. The present study shows that PAB+ cells are widely distributed, are present in varying numbers in different lymphoid organs and that their phenotype varies depending on the organs from which they are isolated. Up to 10 times more cells in PAB+ enriched populations bind antigens as compared to PAB− populations. Comparison of PAB+ with B-1+ cells showed that a high percentage of PAB+ cells are B-1+, but that many PAB+ cells do not express B-1 cell surface markers and, in fact, are B-1−. It is concluded that the B cell population consists of PAB+/B-1+, PAB+/B-1−, PAB−/B-1+, and PAB−/B-1− cells. The presence of PAB+ cells in the thymus points to the possibility that PAB+ cells may carry endogenous host antigens from peripheral tissues to the thymus where they may contribute to immunological tolerance.