This paper describes a method for purification of human myeloma cells. Mononuclear cells from six bone marrow samples and one pleural fluid sample from multiple myeloma patients were incubated with B-B4, a monoclonal antibody that is specific for plasma cells, and the B-B4+ cells were isolated using monosized magnetic beads coated with sheep anti-mouse Ig. With this positive selection method it was possible to achieve primary cultures with more than 99% myeloma cells. The average viability of these cultures was 81%. The B-B4 antibody did not alter proliferation or cytokine production of the myeloma cell lines U-266 and JJN-3. The B-B4+ myeloma cultures did not produce IL-1 and made only small amounts of IL-6 (< 93 pg/ml), whereas the cells remaining after extraction of the B-B4+ cells produced IL-1 (89-350 pg/ml) and large amounts of IL-6 (520-17,000 pg/ml). This indicates that the B-B4+ myeloma cells are not directly responsible for the overproduction of these cytokines in multiple myeloma. This separation technique gave higher purity of myeloma cells than has been previously reported for any negative selection method and is recommended when high culture purity is of critical interest.