The HLA-DP (HI43) antibody recognizes a 28/34-kDa α, β heterodimer glycoprotein named class II major histocompatibility complex (or human leukocyte antigen) DP monomorphic antigen expressed on hematopoietic progenitors, B lymphocytes, monocytes/ macrophages, dendritic cells, langerhans cells, activated T cells, some endothelial and epithelial cells, but not on resting T lymphocytes, erythrocytes and platelets. HLA-DP antigen is also expressed at high levels on B lymphocyte leukemic cells and cells of CML-LBC, at moderate levels on the cells of AML-M1/M2, M4 and M5, but not on the cells of AML-M3 and CML. This antibody can be used as a valuable reagent in diagnosis and classification of leukemias.