We report a patient with acute myelofibrosis (AM) in whom a megakaryocytic origin was demonstrated after conventional microscopy, investigation with monoclonal antibodies directed against the glycoprotein complex IIb/IIIa (CD41a) and the platelet peroxidase (PPO) reaction. Thus, a diagnosis of acute megakaryoblastic leukemia (AMGL) was made. It is now known that this megakaryoblastic proliferation is responsible for myelofibrosis as an increased release of platelet-derived growth factor (PDGF), beta-thromboglobulin (BTG), and platelet factor 4 (PF4) develops because ineffective megakaryocytopoiesis and failure of these clonal populations to store the mentioned substances in their alpha granules. At the time of diagnosis, the plasma concentrations of BTG and PF4 were measured and were found to be high. Thus, an increased PDGF level was indirectly assumed, with the subsequent fibroblast stimulation. After treatment with low dose cytosine arabinoside, a clinical, analytical and histological remission was achieved, with a return of BTG and PF4 values to the normal range. It was therefore concluded that the follow up of these parameters is useful for the diagnosis and the establishment of remission criteria in these patients.