1. A group of patients with essential hypertension was divided into three categories on the basis of the plasma renin activity. 2. There was no correlation between the plasma renin activity categorized as high, normal or low and the duration of hypertension, the incidence of left ventricular enlargement, the blood urea nitrogen, serum creatinine, cholesterol or uric acid respectively. 3. Analysis of data showed that the incidence of cardiovascular events in the hypertensive population correlated with the plasma renin activity only in combination with known risk factors.