A Green function filter operator (H-E.1)(-1) is used within a wave operator iterative method for the computation of interior eigenvalues of large Hamiltonian matrices. Test calculations on a coupled oscillator system show a significant improvement in the convergence of the wave operator iterative method when the filter is used with a one-dimensional active space. Less convincing results are obtained with multidimensional active spaces involving several states in near resonance; other filter functions such as (H-E.1)(-2) seem to be more suitable for this case.