The case of a 60-year-old diabetic patient with a fully developped diabetic glomerulosclerosis in one kidney, but only ischemic lesions in the contralateral one, which was ‘protected’ by a renal artery stenosis, is presented. The only other report of such a peculiar observation was made by Berkman and Rifkin on a patient who died in 1940. Because of the rather high incidence of diabetes and of renal artery stenosis, the scarcity of this ‘experiment of nature’ is astonishing and can be barely explained by a precise timing of the two pathological conditions. Despite rather detailed information on the clinical and paraclinical evolution of the present patient, the exact sequence of events could not be determined with certitude. Both cases bring a strong support for the role of glomerular hyperperfusion-hypertension in the pathogenesis and evolution of diabetic nephropathy and provide a theoretical basis for the importance of keeping the arterial pressure low in di