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eloproliferative disorders (MPD) is believed to be secondary to autonomous unregulated platelet production. Secondary or re-active thrombocytosis (RT) can be observed in a number of clinical circumstances and may be related to persistent produc-tion of some thrombopoietic factors acting on megakaryocytes (MK). The goal of this study is to assess the serum concentra-tions of these cytokines in control subjects and patients with MPD associated with thrombocythemia, RT, and autoimmune thrombocytopenic purpura (ATP). Eleven patients with MPD, five with chronic myeloid leukemia (CML), three with poly-cythemia vera (PCV), two with essential thrombocythemia (ET), one with myelofibrosis, 15 with RT, eight with ATP, and 12 healthy volunteers were enrolled in the study. Serum inter-leukin (IL)-1 β, IL-6, tumor necrosis factor-alpha (TNF), fibro-nectin, intracellular adhesion molecule-1 (ICAM-1), an