A new experimental method of causing apparently sustained hypertension of renal origin is described. The method depends on the production of a source of micro-emboli in the thoracic aorta of rabbits by the insertion of magnesium-aluminum wire, covered by a plastic in which notches have been cut. Thrombus, considered to be formed largely of platelets, forms on the exposed areas of the wire and atrophic lesions subsequently occur along the cortical surface of the kidneys. It is probable that the atrophic lesions are due to repeated episodes of platelet micro-embolism. These lesions resemble the marginal zone of infarcts, which has been suggested as the source of a pressor substance. Proximal to the atrophic lesions, arterioles show a prominent intimal thickening resembling that seen in severe hypertension.