We report on the results of third-harmonic generation (THG) measurements on vapor-deposited thin films of two polyazomethines, poly(nitrilo-1,4-phenylenenitrilomethylidyne-1,4-phenylenemethylidyne) (PNPP) and poly(nitrilo-2,5-azinylnitrilomethylidyne-1,4-phenylenemethylidyne) (PNAP) covering pump energies from 0.6 to 1.4 eV. The THG data show the presence of a strong three-photon resonance centered near 0.9 eV for both samples; additional weaker structure is observed for PNPP near 1.2 eV. The peak values of the third-order susceptibility are 2.8 × 10 −11 e.s.u. for PNPP and 1.8 × 10 −11 e.s.u. for PNAP; off-resonance values are nearly an order of magnitude smaller. We have also obtained the χ (3)(3 ω) spectrum of an oriented PNPP film grown on an obliquely evaporated SiO 2 pattern. An enhancement by nearly a factor of three in the peak nonlinear optical susceptibility is observed relative to that of the unoriented PNPP film, demonstrating that a moderate degree of molecular orientation was achieved.