The effect of oxygen on the electrical properties of PbTe films has been investigated. Oxygen, which presumably is adsorbed on the surface of the film, causes an increase in film resistance, followed by a decrease in resistance with increasing exposure to oxygen. The film which is originally "n" type changes to "p" type in the vicinity of the resistance maximum. The magnitude of the photoresistive and photovoltaic effect varies with the amount of oxygen adsorbed by the film. A model has been presented whereby oxygen removes electrons first from the conduction band, then from trapping states, and finally from the valence band, thereby producing the observed effects.