We established an animal model of radiation-induced skin ulcers in rats irradiated with 35 to 55 Gy y-rays. The pathological changes were observed for 1 year. Immunohistochemical studies were performed on 72 radiation-induced skin ulcer specimens using c-fos and Rb protein polyclonal antibodies. We found that the overexpression rate of c-fos was 45.8% and of Rb was 63.9%. The overexpression of c-fos was mainly seen in the nuclei of activated squamous epithelial cells and in some fibroblasts and endothelial cells of arterioles in the deep part of the skin ulcers. The overexpression of Rb had the same localization. Our results suggest that the changes in c-fos and Rb proteins may be related to the poor healing of radiation-induced skin ulcers.