The ac response of polyaniline thin films on platinum electrodes was measured at different dc potentials during the N-2-fixation in methanol + LiClO4 electrolyte with 0.03 mol L-1 H2SO4 for the first time. The optimum film thickness was found to be 1.5 mu m, N-2-pressure 50 bar and an optimum electrolysis potential of -0.12 V (NHE). The diffusion coefficients for N-2 into the polymer film was found to be (5 +/- A 2)x10(-9) cm(2) s(-1).