Erythrocyte precursor cells reside in the bone marrow, and are part of erythropoesis, the formation of circulating erythrocytes (i.e., red blood cells).
The erythroid progenitor cells develop in two phases: erythroid burst-forming units ( BFU-E) followed by erythroid colony-forming units ( CFU-E); BFU-E differentiate into CFU-E on stimulation by erythropoietin, and then further differentiate into erythroblasts when stimulated by other factors.