Twelve adult rabbits were used to study radiation-induced changes in the urinary bladder by angiographic, microangiographic, light microscopic and scanning electron microscopic methods. Angiographic, microangiographic and light microscopy examinations were performed on 2 animals in which the urinary bladders were not irradiated and on 4 animals in which parts of the bladders received high radiation doses of 60Co. The bladders irradiated in this manner exhibited advanced changes within a shorter time after irradiation than those in an earlier study. In this study a lower dose of irradiation was given over the entire bladder. Otherwise, the radiation changes were similar. Light and scanning electron microscopic studies were carried out on 2 normal and 4 irradiated bladders. In the latter, atrophy of the mucosa, epithelial desquamation, cellular atypisms and ulcerations were observed.