Proerythroblasts, also called pronormoblasts, are the first microscopically recognizable stage of erythropoiesis. They constitute about of nucleated bone marrow cells (myelogram).
With a diameter of 15-20 µm, the pronormoblast is one of the larger cells of the bone marrow. The cytoplasm is narrow and darkly basophilic; often with a clearly limited perinuclear halo (Golgi apparatus). The nucleus has a granular structure and several nucleoli.