We demonstrated the utility of dual parameter analysis of DNA and cytoplasmic immunoglobulin for the detection of minimal residual myeloma cells in bone marrow and peripheral blood. This method is sensitive: even 0.1% of contaminating myeloma cells could be detected in peripheral blood of myeloma patients and in the model experiments using cell lines. This method is useful for the selection of patients undergoing high-dose chemotherapy and autologous blood stem cell transplantation.