Multiple Myeloma remains a largely incurable disease with current therapy. Allogeneic bone marrow transplantation provides an opportunity to add the potential antitumor effect of marrow grafts to those of high dose chemotherapy. One potential strategy for enhancing a graft vs. tumor effect without aggravating graft vs. host disease would be to selectively target an immune response against a defined tumor-specific antigen. The idiotype of the rearranged immunoglobulin gene product of a myeloma can serve as a unique tumor-specific antigen for vaccine development. We are testing the hypothesis that tumor antigen-specific immunity can be adoptively transferred to BMT recipients by active immunization of marrow transplant donors with purified myeloma idiotype protein, conjugated to a carrier protein (KLH) and administered with GM-CSF as an immunological adjuvant.