The polycythemia rubra vera 1 gene (PRV-1 ), a member of the urokinase-type plasminogen activator receptor superfamily, is overexpressed in granulocytes isolated from the peripheral blood of patients with polycythemia vera (PV) and essential thrombocythemia (ET). PRV-1 overexpression is the first reliable molecular marker of these myeloproliferative disorders, and its detection allows us to discriminate PV and ET from secondary erythrocytosis and thromb- ocytosis. PRV-1 overexpression can be investigated by several techniques, including Northern analysis, reverse-transcription (RT)-polymerase chain reaction (PCR), and real-time PCR. Among these, RT-PCR is the most rapid, reliable, and feasible method for the detection of PRV-1 overexpression in highly purified peripheral blood granulocytes.