Erythropoietin is a glycoprotein hormone produced in the kidneys and to a lesser extent in the liver which regulates the proliferation and differentiation of erythroid progenitor cells. The gene for erythropoietin is well conserved and the hormone is always present in the plasma even in the renoprival state, emphasizing its important physiologic role. Failure to produce adequate quantities of erythropoietin leads to severe anemia, a situation most often encountered in patients with end stage renal disease. With the application of recombinant DNA technology, the gene for erythropoietin has been molecularly cloned, sequenced and expressed in a biologically active form in mammalian cells. In recent clinical trials, the recombinant hormone has been demonstrated to correct anemia in patients with severe end stage renal disease and alleviate their transfusion requirements.