Thrombopoietin (TPO) is a recently described novel cytokine produced in both liver and kidney. TPO protein secreted is glycoprotein with relative molecular mass of over 35 ku.Human and mouse mature TPO consist of 332 and 335 amino acid residues respectively. TPO receptor is related to c-Mpl which is a member of the hematopoietin receptor superfamily. TPO not only regulates the proliferation and differentiation of megakaryocyte progenitor cells, but also regulates the production of platelets.