Aluminium surfaces abraded in oxygen or air ambient show a temporary photoelectric response at longer wavelengths than that of the threshold for clean aluminium (2900 Å). This effect has been studied over a range of temperatures from 195°K to 500°K and for different gas pressures, using a silver-magnesium type electron multiplier as detector. No so-called `exo-electron' emission has been observed under dark conditions during or after abrasion. The study of the rise and decay of the sensitized photoelectric emission provides a method of investigating the very early stages in the oxidation of metals such as aluminium and zinc. A tentative model suggests that oxygen vacancies or interstitial metal atoms in the developing oxide layer provide electron levels above the Fermi level of the metal, from which they are ejected by photon absorption. Progressive oxidation reduces the ability of these electrons to reach the surface where there is a further inhibiting effect due to the negatively charged adsorbed oxygen layer.