Abstract. We consider natural complex Hamiltonian systems with n degrees of freedom given by a Hamiltonian function which is a sum of the standard kinetic energy and a homogeneous polynomial potential V of degree k > 2. The well known Morales-Ramis theorem gives the strongest known necessary conditions for the Liouville integrability of such systems. It states that for each k there exists an explicitly known infinite set M k ⊂ Q such that if the system is integrable, then all eigenvalues of the Hessian matrixThe aim of this paper is, among others, to sharpen this result. Under certain genericity assumption concerning V we prove the following fact. For each k and n there exists a finite set I n,k ⊂ M k such that if the system is integrable, then all eigenvalues of the Hessian matrix V ′′ (d) belong to I n,k . We give an algorithm which allows to find sets I n,k .We applied this results for the case n = k = 3 and we found all integrable potentials satisfying the genericity assumption. Among them several are new and they are integrable in a highly nontrivial way. We found three potentials for which the additional first integrals are of degree 4 and 6 with respect to the momenta. MSC2000 numbers: 37J30, 70H07, 37J35, 34M35.