THPO (Thrombopoietin), also known as megakaryocyte growth and development factor (MGDF), is a glycoprotein hormone produced by the liver and kidney which regulates the production of platelets. It stimulates the production and differentiation of megakaryocytes, the bone marrow cells that bud off large numbers of platelets. Megakaryocytopoiesis is the cellular development process that leads to platelet production. THPO is a humoral growth factor necessary for megakaryocyte proliferation and maturation, as well as for thrombopoiesis. This protein is the ligand for MLP/C_MPL, the product of myeloproliferative leukemia virus oncogene. Recombinant human THPO, fused to His-tag at C-terminus, was expressed in insect cell and purified by using conventional chromatography techniques.