Introduction Investigations of the pathogenesis and treatment of diabetic retinopathy have been handicapped by the lack of an acceptable model of the retinopathy in animals made diabetic experimentally. Although various retinal disorders have been reported in such animals, the lesions have remained unconfirmed or of uncertain relationship to the retinopathy of human diabetes. Retinal capillary aneurysms have been clearly demonstrated by Patz and Maumenee1 in a spontaneously diabetic dog, and recently by Hausler and coworkers2 in an experimentally diabetic dog having a complex history. Their work has established that man is not uniquely susceptible to the retinopathy, but whether the lesions are a result of diabetes, or of some genetic or other disorder attending diabetes has not been clarified. In the following study, retinopathy comparable to that of diabetes in man has been found to develop in three dogs as a result of either alloxan or metasomatotropin diabetes.