Serum thrombopoietin (TPO) levels in patient with amegakaryocytic thrombocytopenia is much higher than those with immune thrombocytopenic purpura. The evidence that serum TPO levels are regulated by megakaryocyte mass - Mukai, H Y; Kojima, H; Todokoro, K; Tahara, T; Kato, T; Hasegawa, Y; Kobayashi, T; Ninomiya, H; Nagasawa, T; Abe, T (Thromb Haemost (in press).)