Experiments will continue in the stroke prone rat to assess the results of interference with coagulation in the clinical and pathologic pictures. New experiments will be initiated on the effects of antihypertensive agents, initially reserpine, on the vascular change in this strain. Experiments will be continued on the permeability of the aortic wall to various tracer substances to determine whether angiotensin acts by its hypertensive effect or in other ways. Studies on the turnover of aortic endothelium, morphologic changes in the endothelium, and permeability of the aortic wall will be commenced in rats with high renin hypertension is unduly damaging to blood vessels can be sustained.