We have studied retroviral-mediated gene transfer into human myeloma cells. Bone marrow cells were obtained from four patients with advanced myeloma, where the marrow was heavily infiltrated with myelomatous plasma cells. Myeloma cells were isolated by immunomagnetic separation, using the high-affinity B-B4 monoclonal antibody. Following separation, cells were transduced with the LN retroviral vector, which carries the gene for neomycin phosphotransferase, by incubation in cell-free supernatant with or without a growth-factor combination of IL-3, IL-6 and SCF. After infection, the cells were cultured for 9 d in RPMI-1640 and 10% FCS, either in the presence or absence of the neomycin analogue G418. Transduction efficiency was 1.5-3.8%, when compared to the number of cells at initiation of the culture, and 5.0-50.0% when compared to the number of surviving infected cells cultured without G418. The gene transfer rate was similar whether or not growth factors were present during the retroviral infection. These preclinical data provide evidence that retroviral-mediated gene transfer into human myeloma cells is feasible, and form part of the basis for current clinical studies of gene marking of bone marrow or peripheral blood progenitor cells before autologous stem cell transplantation in multiple myeloma.