the relationship between the level of arterial blood pressure and the development of hypertensive complications is one of the conspicuous difficulties in current concepts of the natural history of essential hypertension. That cardiovascular complications of hypertension are generally more prevalent with the higher levels of blood pressure is recognized. Published data, 1-3 however, invariably include a substantial proportion of cases in which casual blood pressures* were considerably elevated, yet hypertensive complications did not develop, as well as cases in which complications occurred although arterial pressures were only moderately increased. These apparent inconsistencies in the course of the illness lead one to ask how closely are hypertensive complications related to the level of blood pressure? To what extent are the discrepancies between casual blood pressure and clinical