Theoretical expressions describing the photoelectric emission from a metal surface are derived, taking account of the dependence, established by Bardeen, of the effective surface barrier on the momentum of the impinging electron, due to exchange and correlation forces in the interior. This generalization reduces by a significant factor the magnitude of the theoretical expression for the absolute photoelectric yield. The shapes of the energy and spectral distributions of emitted photo-electrons are essentially unchanged, so that certain well-known disagreements between theoretical and observed distributions near the threshold remain unexplained. The influence of the transmission coefficient of the surface potential barrier on the photoelectric properties of a metal is discussed and an experiment is proposed for determining directly the variation with energy of the transmission coefficient, thus leading to information concerning the shape of the barrier.