Lysozyme (LZ) is a cationic antimicrobial peptide of 14 kDa. Lysozyme is stored in primary but predominantly in specific (secondary) granules of neutrophils. It cleaves peptidoglycan constituents of the bacterial cell wall and can bind LPS. The epitope recognized by antibody LZ-2 is expressed by virtually all myeloid cells including normal and malignant granulocytes and monocytes. In normal myelopoiesis LZ can first be detected at the myeloblast stage where it appears somewhat later than MPO expression. The LZ-2 antibody permits the identification and enumeration of human myelomonocytic cells using flow cytometry.