The HLA-DP (HI43) antibody recognizes a 28/34-kDa ?, (B) heterodimer glycoprotein named class II major histocompatibility comple, Xenopus/Amphibian, (or human leukocyte antigen) DP monomorphic antigen e, Xenopus/Amphibian,pressed on hematopoietic progenitors, B lymphocytes,Mouse,onocytes/ 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 e, Xenopus/Amphibian,pressed at high levels on B lymphocyte leukemic cells and cells of CML-LBC, at moderate levels on the cells of AML-M1/M2,Mouse,4 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.