Daily doses of 0.2 mg of Daldosterone-21-acetate in sesame oil caused a mild type of hypertension without vascular disease in uninephrectomized rats given tap water or 1 % saline to drink. Renal secretion of pressor substances ceased and renal content decreased following aldosterone plus salt or water. Injection of partially purified renin to animals pretreated with aldosterone plus salt caused a syndrome similar to the DCArenin disease which is characterized by occlusive glomerular lesions, renal failure, water retention, hemorrhages and acute vascular lesions. The similarity of these symptoms and lesions to those seen during experimental malignant hypertension supports the hypothesis that high blood levels of renin and aldosterone may have some pathogenic significance in clinical malignant hypertension.