The photoelectric yield of evaporated KCl films was measured for photon energies from 7 to 14 eV. A gradual rise of photoelectron emission with time was observed under steady ultraviolet excitation of approximately 8 eV. In the presence of strong biasing radiation (visible light), the gradual rise of photomission did not appear. An attempt is made to explain the transient enhancement in terms of electron emission from newFcenters formed by excitons.