Six patients in whom "essential hypertension" led to nephrosclerosis and kidney failure received kidney transplants from normotensive donors. After an average follow-up of 4.5 years, all were normotensive and had evidence of reversal of hypertensive damage to the heart and retinal vessels. These six patients, all of whom were black, and six control subjects matched for age, sex, and race were admitted to the General Clinical Research Center for 11 days for observation of their blood pressure and their responses to salt deprivation and salt loading. Mean arterial pressure (±S.E.M.) among the patients who had previously had essential hypertension was similar to that of the normal controls (92±1.9 vs. 94±3.9; P not significant), and both groups had similar responses to salt deprivation and salt loading. Thus, essential hypertension in human beings is shown to be similar to the hypertension seen in spontaneously hypertensive rats in that both can be corrected by transplantation of a kidney from a normotensive donor. This observation supports the concept of the primacy of the kidney in causing essential hypertension. (N Engl J Med 1983; 309:1009–15.)