Erythropoietin, or its alternative erythropoetin (/ɨˌrɪθrɵˈpɔɪtən/, or /ɨˌriːθrɵ-/) or EPO,'s a glycoprotein hormone that controls erythropoiesis, or red blood cell production. It's a cytokine for erythrocyte (red blood cell) precursors in the bone marrow. Also called hematopoietin or hemopoietin, it's produced by the peritubular capillary endothelial cells in the kidney, and's the hormone that regulates red blood cell product… (More on Erythropoietin)