Myeloblasts are the first clearly visible light microscopic maturation stage of granulopoiesis. They constitute about of nucleated bone marrow cells (myelogram).
Myeloblasts have a nucleus with very fine chromatin and several clear nucleoli. The cytoplasm is thin, without granules and basophilic. A perinuclear halo is usually visible which corresponds to the Golgi apparatus. Myeloblasts are approximately 15-16 µm in diameter.