We have studied the effects of a constant external electrostatic field on the photoemissive characteristics of thin films of iron. The thin films were obtained by thermal evaporation and condensation on a silica substrate. Thickness was between 0.5 and 110 nm. The direction of the field is perpendicular to the surface of the film; its intensity varies by a few V m−1at 510 000 V m−1. With all the films, the greater the field is, the lower the work function is. The value of this lowering depends on the thickness and structure of the film. It is maximum in absolute value and equal to about 0.07 eV for a thickness of about 2 nm. When the field varies, the photoionization coefficient remains constant within measurement precision for the same film. A possible interpretation, based on the variations of the electrostatic double layer on the surface, is suggested.