Polymorphic HLA-DQ (DC/MB) determinants appeared to be not expressed on human hematopoietic progenitor cells (HPC), using several murine monoclonal and human polyclonal antibodies in a complement-dependent cytotoxicity (CDC) assay. Since mature HLA-DR-positive malignant lymphoma cells prove to be HLA-DQ positive, an attempt was made to remove clonogenic neoplastic DQwl-positive B cells selectively from DQwl-positive marrow samples without affecting hematopoietic progenitor cells. Using a combination of a clonogenic tumor cell assay, an HPC culture assay, and a mixed-tumor-cell-HPC culture assay, selective elimination of more than 98% of clonogenic neoplastic cells from tumor-cell-contaminated bone marrow suspensions was achieved with monoclonal anti-DQ antibodies and complement without depletion of HPC. These results indicate that anti-HLA-DQ antibodies can be used in autologous bone marrow transplantation to deplete the bone marrow cell suspension of DQ-positive malignant cells.