Neutrophil polymorphonuclear leukocytes (PMNs) contain two principal types of granules. Azurophil granules appear early in neutrophil development and contain lysosomal enzymes, lysozyme, and myeloperoxidase (MPO). Specific granules are formed later, lack MPO and hydrolases, but contain lactoferrin and the remainder of the cell's complement of lysozyme. Consequently, specific granules may be conveniently detected at the electron-microscopic (EM) level by the cytochemical demonstration of their lack of MPO, while at the optical level their presence can be inferred from their positive immunocytochemical staining for lactoferrin with the use of specific antiserums.