The criteria for the chance of detecting ET based on the carrier of the polymorphic marker JAK2V617F and W515L MPL were studied by comparison with patients with PMF and IP. In the group of ET patients and in the comparison groups in patients with PMF and PV, the actual distribution of genotypes of these polymorphisms did not deviate from the expected ones, at the Hardy-Weinberg equilibrium (χ2=3.84; p<0.05).