1. The arteriolar lesions of rats with deoxycorticosterone (DOCA)—salt hypertension have been studied by colloidal carbon injection and light- and electron-microscopy.
2. Colloidal carbon particles enter the media of arterioles to form focal deposits when hypertension develops.
3. The focal lesions are similar to those seen after angiotensin infusion or renal artery constriction. They are characterized by endothelial damage and plasma deposition in the media.
4. Heavy deposition of carbon in the glomeruli of DOCA-treated animals was found to be caused by increased mesangial uptake and not by hypertensive vascular damage.
5. Angiotensin II concentrations fell during the development of hypertension and vascular lesions. The renin—angiotensin system was not implicated in the development of vascular damage in this form of hypertension.