Recent observations that clonogenic cells in myeloma express CD20 (Kiel et al, 1999, Rottenburger et al, 1999) and that their growth could be inhibited in vitro by rituximab, an anti-CD20 antibody (Matsui et al, 2004), provides a rationale for using CD20-directed therapy in patients with myeloma. Moreover, CD19+/CD20+ clonotypic cells appear to be more refractory than CD19-/CD20- cells to commonly used chemotherapy regimens in myeloma including high dose therapy with stem cell transplant (Kiel et al., 1999, Rottenburger et al, 1999). Therefore, CD20+ directed treatment of myeloma would complement chemotherapy by targeting chemoresistant clonogenic myeloma cells.