Generically hamiltonian systems are non integrable o However there are few tools in order to prove that a given system is nonintegrableo For two degrees of freedom the usual methods rely upon the appearance of tran~ versal homoclinic or heteroclinic orbitso The transversal character is shown through evaluation of integrals along orbitso Such computation requl res the knowledgement of a one parameter family of periodic orbits and an explicit solution for the unperturbed (integrable) caseo Oue to the dependence of the form exp(-C/epsilon K) of the angle measuring transversality with respect to the perturbation parameter, none of the approximations of pertu~ bation theory is enough to establish nonintegrabilityo