In granulopoiesis, promyelocytes follow after myeloblasts. Their characteristic feature is primary or azure granules. They constitute about of nucleated bone marrow cells (myelogram).
Promyelocytes are large cells and measure 22-25 µm in diameter. They are therefore relatively easy to recognize. The nucleus is round and usually eccentric. The chromatin is fine and shows one or several clear nucleoli. The cytoplasm is large in volume, basophilic and contains coarse red granules (primary or azure granules).