Thrombopoietin (TPO) is the principle physiologic regulator of megakaryopoiesis and platelet production. TPO act in synergy with many other cytokines such as IL-6, IL-3, IL-11 and erythropoietin. Administration of rHu-TPO to human causes an increase in circulatory platelets in a dose dependant manner. TPO in synergy with erythropoietin has the ability to enhance erythroid proliferation. Serum TPO levels in various disorders accompanied with thrombocytopenia are variable and may correlate with megakaryocyte mass rather than platelet count. Many clinical trials were done to use TPO in treatment of thrombocytopenia due to chemotherapy, irradiation, leukemia and aplastic anemia.