The progression of small vessel renal vascular disease was studied in inbred Dahl salt-sensitive (SS/Jr) and salt-resistant rats with acute hypertension induced by a high salt diet. Corrected cross-sectional areas of wall (WAC) and lumen were measured by planimetry and histologic staining for fibrin, hyalin deposition, and elastic lamellae was performed. In SS/Jr rats on the high salt diet, the hallmarks of malignant hypertension (fibrinoid necrosis, hyperplastic and necrotizing arteritis) appeared by week 2 and were intensified after 4 weeks on the high salt diet. Renal vascular lesions from SS/Jr rats were characterized by: hyperplasia and/or hypertrophy of medial smooth muscle cells; intimal proliferation; fibrin, basophilic mucoid, and hyalin deposition within the the subendothelial space and media; variable adventitial fibrosis; and accumulation of mononuclear inflammatory cells in the adventitia and media. Interlobular arteries from both rat strains exhibited significantly increased cross-sectional areas over time for all measured parameters. Intralobular arterioles from both rat strains exhibited significantly increased cross-sectional areas over time for all measured parameters except lumen from SS/Jr rats. For SS/Jr rats, increased WAC from both arterial divisions correlated positively with systolic blood pressure, but not body weight. In salt-resistant rats, increased WAC from both arterial divisions correlated positively with body weight, but not systolic blood pressure. We concluded that the rapid increase in WAC from SS/Jr rats could not be attributed solely to the normal growth of the rat. With the development of acute hypertension in the SS/Jr rat, these results demonstrate the potential usefulness of this model to investigate the pathogenesis of similar renal vascular alterations which are observed in man.