Résumé : The π--12C elatic differential cross sections have beenmeasured at three kinetic energies around the ( 3 2, 3 2) pion-nucleon resonance, namely 120, 180 and 260 MeV, in the small-angle region [t ≤ 18 000 (MeV/c)2] where the interference between Coulomb and nuclear amplitudes is most pronounced. An expression for the relative phase between Coulomb and nuclear amplitudes has been derived which takes into account a variation linear in t of the nuclear phase. Using this formula, the real part of the forward nuclear amplitude has been deduced from the data at each energy. The results are in good agreement with the predictions of pion-nucleus forward dispersion relations. The nuclear phase seems to vary significantly at 260 MeV. © 1969.