SUMMARY Malignant hypertension was induced in rats by aortic ligation above the left renal artery. After 7- and 28-day periods of hypertension, the characteristics of the vascular disease were studied and the kidney below the aortic ligation was removed. The blood pressure and the vascular disease were reexamined at the end of the first and fourth weeks after nephrectomy. The evolution of the vascular disease was assessed in the contralateral kidney, in the heart, and in the superior mesentery. The results obtained allowed the following conclusions: 1) when the predominant lesions are of fibrinoid necrosis and moderate intimal hyperplasia without fibromucoid changes (initial phase), the hypertension and the hypertensive vascular disease are completely reversible after the nephrectomy; 2) when the predominant lesions are proliferative endarteritis with fibromucoid changes (chronic phase), neither the hypertension nor the vascular disease are reversible after the left nephrectomy and during the period of follow-up. Therefore, the type of vascular lesion seems to be one important determinant of the reversibility of the hypertensive process after nephrectomy.