The human erythropoietin receptor (EpoR) is located on stem and mature cells of the hematopoietic system. When activated by its native ligand, erythropoietin (Epo), EpoR mediates proliferation and maturation of the erythroid precursor cells leading to expansion of red cell populations. Human recombinant Epo is currently used for treatment of patients undergoing erythrocyte depletion due to dialysis for kidney failure.