JAK2 V617F mutation is found in a high proportion of MPD patients. We developed a quantitative assay for the detection of the JAK2 mutation and demonstrated its clinical utility in MPD patients who underwent SCT. Sixty percent of the patients were JAK2 V617F positive prior to the SCT (mean mutation levels 74%, range 16-98%). After the procedure, the mutation levels progressively decreased and were in correlation with the donor-recipient chimerism status (r=0.97, p<0.001). At a median follow up of 16 months (range 2-58), 9/15 patients are alive and in CR. The levels of the JAK2 V617F mutation reached 0% in all surviving patients.