Erythropoietin (EPO) is the principal factor that regulates erythropoiesis by stimulating the proliferation and differentiation of erythroid progenitor cells. Cytolab's Human EPO containing 165 amino acid residues has a predicted molecular mass of approximately 21 kDa. As a result of glycosylation, the recombinant protein migrates with an apparent molecular mass of 30.4 kDa.