Kaon B - parameter with N F = 2 dynamical Wilson fermions

We present a preliminary study of the neutral kaon mixing bag parameter B K using two flavors of dynamical Wilson fermions. We determine the matrix element of the relevant ∆S 2 operator by using both the conventional approach and the so called " non-subtraction method " , and find that the latter leads to results with smaller uncertainties. After having implemented non-perturbative renormalization, we study the dependence of B K on the sea quark mass. At our relatively heavy values of quark masses (M P M V ³ 060 ¤075) such a dependence is found to be negligible and the results, within the statistical accuracy, are consistent with a quenched determination. As a preliminary result for the renormalization group invariant parameter we quotê B K 102´20µ.