ESTABLISHMENT of experimental hypertension by compression of one or both renal arteries with a metal clamp1 directed attention to lesions of main renal arteries as causes of hypertension in man. Some investigators2 believed that they could demonstrate at autopsy a high incidence of arteriosclerotic narrowing in fixed preparations of renal arteries from hypertensive patients. However, Lisa and associates3 could not show a relation between the level of arterial pressure during life and the caliber of the renal arteries in fresh preparations. Yuille4 reviewed the relation between lesions of main renal arteries and hypertensive disease and discounted the participation of renal arteriosclerosis in the genesis of this condition. He pointed out that the lesions of large vessels were commonly associated with intrarenal arteriolar sclerosis and that both were presumably results and not causes of hypertensive disease. Had the arterial lesions been primary, then, as in experimental renal hypertension in rats,5 arteriolar