CD38 is a novel multifunctional ectoenzyme widely expressed in cells and tissues especially in leukocytes. CD38 also functions in cell adhesion, signal transduction and calcium signaling. CD38 antigen is an integral membrane glycoprotein, M.W. 45 kD. The CD38 antigen is present on approximately all pre-B lymphocytes, plasma cells and thymocytes. CD38 antigen is also expressed on activated T Lymphocytes, NK Cells, monocytes, myeloblasts and erythroblasts. CD38 is co-expressed on CD34+ cells,but is not expressed on pluripotent stem cells. CD38 antigen is present on T and B lymphoblastic leukemia (ALL), Burkitts' lymphoma, multiple myeloma and acute myeloid leukemia (AML).