The purpose of this study was to investigate the frequency of JAK2V617F gene mutation in patients with polycythemia vera (PV) and to compare the results with the presence of endogenous erythroid colony (EEC) formation.Peripheral blood and bone marrow samples of 28 patients with PV were analyzed. The diagnosis of PV was established according to the bone marrow criteria of the World Health Organization (WHO). Mutation of JAK2V617F was determined by allele-specific PCR (AS-PCR) analysis. For detection of EEC formation we used assays of human clonogenic heamatopoietic progenitor cells with agar-leukocyte conditioned medium (Agar-LCM) without recombinant human erythropoietin (EPO).Mutation was found in the samples of the peripheral blood in 26/28 (92.9%) PV patients. EEC formation was obtained in the sample of bone marrow in 27/28 (96.4%) PV patients. In 25/28 (89.2%) patients we detected presence of EEC formation and mutation of JAK2V617F at the same time.Considering these results, we hypothesized that the EEC formation observed in myeloproliferative disorders could be partially due to the JAK2-dependent activation signaling pathway.