Specific binding of antigens to the surface immunoglobulin M (sIgM) triggers B cells with several biochemical events involved in receptor-mediated signal transmission for proliferation and differentiation into antibody-producing cells. Recent studies with the Digitonin lysis method identified the sIgM-associated component, IgM-alpha (B34)/Ig-beta, as the possible candidate for the transducer molecule(s) in the immunoglobulin receptor-mediated signal transmission. The 34 kd protein (B34 or IgM-alpha) of this component is suggested to be encoded by the B cell-specific mb-1 gene. We prepared monoclonal antibodies which recognize the mb-1 gene product (MB-1) and studied the functional role of MB-1 in the signal transmission in B lineage cells. Using murine pre-B lymphoma cells (18-81 and 70Z/3), we demonstrated the early phase increase of the intracellular [Ca2+]i concentration and the subsequent inhibition of the proliferation by the monoclonal anti-MB-1 antibody (11-18-5). These results clearly demonstrate signal transmission through the surface MB-1 molecule on B lineage lymphomas. This MB-1-mediated signal transmission in pre-B cell lines would suggest an alternative function of MB-1 acting at the pre-B cell stage.