Long-term bone marrow cultures (LTBMC) were initiated with marrow aspirate cells from 12 patients with multiple myeloma (MM) using the Dexter system. The myeloid and the neoplastic myeloma cell growths were evaluated for up to 6-9 weeks. Our results demonstrate the development of an adherent layer capable of supporting normal granulopoiesis with a concomitant drop in the growth of myeloma cells. The B lymphocyte monoclonal proliferative compartment was also studied with bromodeoxyuridine (Brdurd), an analog of thymidine incorporated during the S-phase, and the labeling index was calculated. The ability to form myeloma stem cell colonies in a modified plasma clot short-term assay was also evaluated. The results confirmed that the neoplastic B lineage compartment was not able to grow in Dexter's system for more than 4 weeks in 11 of 12 cases studied, with the disappearance of Brdurd-positive cells after two weeks, whereas LTBMC were able to sustain the growth of myeloid progenitors. These data indicate the potential applicability of this culture method in selecting normal hematopoietic progenitors from patients with multiple myeloma. This approach can have significant implications for aggressive treatment of patients with multiple myeloma, especially in trials involving autologous bone marrow transplantation (ABMT).