SummaryHigh blood pressure has a deleterious effect on the kidney. It significantly modifies renal handling of water and electrolytes partially, at least, as a result of haemodynamic changes in the kidney. These disorders, which are observed only under conditions of maximal stimulation, are of little interest to the clinician.Hypertension ultimately accelerates the ageing process of the kidney resulting in benign nephrosclerosis. This latter condition is not usually a cause of severe renal failure.Severe elevation of blood pressure occasionally induces malignant hypertension. This condition is characterized by necrotizing angeitis associated with subacute renal failure. Prompt and efficient hypotensive therapy may prevent or stabilize renal insufficiency. In a few cases, a return of normal renal function has been observed despite initial acute renal failure. The prognosis of malignant hypertension is determined largely by th2 degree of renal insufficien cy prevailing when hypotensive therapy is started. At first, lowering blood pressure may decrease glomerular filtration rate. In the long run, however, renal function improves.