CD33 or Siglec-3 is a 67 kD glycosylated transmembrane receptor expressed on myeloid-specific cells (1,2). In the past, CD33 was only used for flow cell cytometry. Recently, a CD33 for paraffin-embedded tissues has been developed and has been used to phenotype acute myelogenous leukemias (1,2). In cases of acute leukemia, the CD33 antibody showed equivalent results by immunohistochemical analysis compared with flow cytometric analysis (1). The CD33 antibody was also found to be a useful marker in the workup of myeloid sarcomas (1,3). In normal bone marrow trephine biopsies, clone PWS44 stains myeloid, myelomonocytic hemopoiesis and mature macrophages; cells of the erythroid and megakaryocytes series are negative for CD33 (1). In conclusion, CD33 antibody may be a useful marker as part of an antibody panel for the identification of acute leukemias, myeloid proliferative disorders and myeloid sarcomas on paraffin-embedded tissue samples (1-3).