Clinical diagnosis of the myeloproliferative disorders (MPD) has previously been based on clinical data and bone marrow morphology due to lack of specific molecular markers. The discovery of JAK2 V617F mutation has shed light on understanding of the molecular pathways involved in the pathogenesis of the myeloproliferative disorders. The thrombopoietin receptor gene (MPL) is expressed in megakaryocytes and exhibits the gain of function point mutation in approximately 5% of MPDs. Several research groups have used real-time PCR to detect and quantify the presence of JAK2 V617F mutation. We report here a highly specific real-time assay based on the TaqMan((R)) technology to detect the MPL W515L mutation with high sensitivity from the patient's blood. This assay can be easily performed together with the JAK2 V617F mutation assay on the same real-time PCR reaction plate.