Erythropoietin receptor(EPOR) is a 66 kDa peptide and is a member of the cytokine receptor superfamily that contains aW-S-X-W-S motif and four cysteine residues in the extracellar domain. Erythropoietin (EPO) is the regulator of red blood cell formation. Its receptor (EPOR) is now found in many cells and tissues of the body. EpoR is also shown to occur in tumor cells and Epo enhances the proliferation of these cells through cell signaling. EPOR antagonist can reduce the growth of the tumor in vivo. EpoR is expressed in high or low affinity forms, but the high-affinity receptor is likely the more physiologically relevant class. A peak in EpoR expression occurs on erythroid progenitor cells at the CFU-E/proerythroblast stage, but subsequently decreases following maturation and differentation; EpoR cannot be detected on reticulocytes.