A theory of edge enhancement was developed to describe xeroradiographic images of linear step objects. The theory is shown to give an accurate description of the relationship between edge enhancement, subject contrast, radiation exposure, selenium charging potential and developer bias potential. An optimal trasmitted x-ray exposure exists which gives the maximum edge enhancement. For low contrast structures, this same optimal exposure yielded the most acceptable images as judged subjectively. This finding led to the successful application of automatic exposure termination in mammographic examinations using xeroradiography.