Dario Bambusi , Giuseppe Gaeta Invariant tori for non conservative perturbations of integrable systems (464K, Gzipped PostScript) ABSTRACT. We prove some results on the persistence of invariant tori for non hamiltonian perturbations of integrable systems. We also obtain persistence for the case where the unperturbed torus is resonant. In such a case the persistence of invariant tori is ensured for $\epsilon$ (the size of perturbation) small, but outside of a neighbourhood of zero.