We measured the serum levels of GDF15 in 14 healthy volunteers and in 128 patients with various hematopoietic malignancies, including acute myeloid leukemia (AML; n = 7), MDS (n = 28), chronic myelogenous leukemia (CML, n = 4), PMF (n = 13), PV (n = 22), ET (n = 20), MM (n = 10), malignant lymphoma (ML; n = 14), acute lymphoblastic leukemia (ALL; n = 3), and adult T-cell leukemia (ATL; n = 7). The gene discussed is GDF15; the disease is essential thrombocythemia.