Abstract. We prove an existential finiteness result for integrals of rational 1-forms over the level curves of Darbouxian integrals.1. Limit cycles born by perturbation of integrable systems 1.1. Poincaré-Pontryagin integral. Limit cycles (isolated periodic trajectories) of polynomial planar vector fields can be produced by perturbing integrable systems which have nested continuous families of non-isolated periodic trajectories. The number and position of limit cycles born in such perturbations is determined by the number and position of isolated zeros of the Poincaré-Pontryagin integral of the dissipation form along the closed periodic orbits of the non-perturbed integrable vector field. The infinitesimal Hilbert problem is to place an upper bound for the number of isolated zeros of this integral. This problem was repeatedly formulated as a relaxed form of the Hilbert 16th problem by V. Arnold [1].Instead of polynomial vector fields, it is more convenient to deal with (singular) foliations of the real plane R 2 by solutions of rational Pfaffian equations θ = 0, where θ is a 1-form on R 2 with rational coefficients (since only the distribution of null spaces of the form θ makes geometric sense, one can always replace the rational form by a polynomial one). The foliation F is (Darbouxian) integrable, if the form is closed, dθ = 0. An integrable foliation always has a "multivalued" first integral of the form f (x, y) = exp r(x, y) · j p j (x, y) λ j , where r(x, y) is a rational function and p j polynomials in x, y, which are involved in the in general non-rational powers λ j . A particular case of the integrable foliations consists of Hamiltonian foliations defined by the exact polynomial 1-formIf L ⊂ R 2 is a compact smooth leaf (oval) of an integrable foliation θ = 0 belonging to the level curve {f = a} ⊂ R 2 , then all nearby leaves of this foliation are also closed and form a continuous family of ovals belonging to the level curves {f = t}, t ∈ (R 1 , a). The ovals from this family, denoted by L t , are uniquely parameterized by the values of the real variable t varying