1. Intra-arterial pressure, renal plasma flow and glomerular filtration rate were estimated in thirty-two patients with benign essential hypertension. In twenty cases plasma renin concentrations were also determined. Variability of blood pressure was estimated by automatic indirect pressure recording.
2. There was an even distribution between high and low values of renal vascular resistance and filtration fraction. Variability of blood pressure was inversely related to renal vascular resistance.
3. In five patients plasma renin concentration was found to be abnormally low both in the recumbent and in the 45° tilt position.
4. Plasma renin concentration was related to renal blood flow, renal vascular resistance, filtration fraction and variability of blood pressure.
5. The results suggest that in hypertension renin release is suppressed by an increase in intravascular pressure at the level of the juxtaglomerularcells. The extent of renin suppression seems to be related to the stage of hypertensive disease.