The monoblast is the first stage of monocyte-macrophage maturation. From one to four nucleoli may be visible. The nucleus may be either central or eccentric and it may show evidence of indentation or folding. The cytoplasm is agranular, stains moderately to lightly basophilic, and often has an intensely stained periphery and a prominent perinuclear zone.
Monoblasts never appear in the normal peripheral blood.