We describe two monoclonal antibodies, HH1 and HH2. Both reacted selectively with surface immunoglobulin (sIg)-positive human B cells. Both antibodies stained on average 7-8% of peripheral blood mononuclear cells. They have not been found to react with cells or cell lines of other haematopoietic cell lineages, except that HH2 was positive on a small percentage of cells of the erythroid cell line K562. The molecular weight of the HH1 antigen was 95 kD, as established by Western blotting. Neither of these two antibodies reacted with Ig determinants, Fc receptors, complement receptors, or known class-I or class-II molecules. A combination of these antibodies was used in a direct panning technique for high-yield enrichment of normal B lymphocytes from peripheral blood. The enriched B cells could be further purified by lysis of T cells (final yield, on average 72 +/- 8% of initial B cells) or by a second panning (yield, 35 +/- 11%). The purified B cells contained less than 1% contaminating T cells and less than 0.5% monocytes and were used in an assay for B-cell-stimulating factor which they showed a normal and very reproducible proliferative response.