(premyelocyte) n. the developmental stage of a *granulocyte (a type of white blood cell) between the *myeloblast and the *myelocyte. It has abundant cytoplasm that, with *Romanowsky stains, appears blue with reddish granules. Promyelocytes are normally found in the blood-forming tissue of the bone marrow but may appear in the blood in a variety of diseases. See also granulopoiesis.... promyelocyte