Recently, several research groups have demonstrated the existence of a point mutation in JAK2 in most patients with polycythaemia vera (PV), and approximately half of patients with essential thrombocythaemia (ET) and primary myelofibrosis (PMF) which are subtypes of myeloproliferative disorder (MPD) [2-4]. The gene discussed is JAK2; the disease is acquired polycythemia vera.