Summary:We report a 62-year-old male who underwent non-myeloablative allogeneic peripheral blood stem cell transplantation (PBSCT) because of his life-threatening severe pancytopenia due to refractory Waldenström's macroglobulinemia. This therapy was performed safely and he made a marked recovery from his cytopenia that had not been improved with any other therapy. Bone marrow aspirates showed post-transplant mixed chimerism during engraftment, and became completely donor-derived after a series of GVHD symptoms, without subsequent donor lymphocyte infusion. Our results suggest that non-myeloablative allogeneic PBSCT could be a good alternative for patients suffering from multidrug resistant Waldenström's macroglobulinemia. Bone Marrow Transplantation (2001) 28, 609-611.