Plasma renin activity (p.r.a.) of hepatic vein and peripheral vein blood was determined in 19 patients (renovascular hypertension - 12, essential hypertension - 6, hepatic cirrhosis - 1). The mean hepatic vein p.r.a. was 70% of the value obtained in peripheral blood. The role of hepatic inactivation of renin in man is discussed. The renin-angiotensin system can be influenced by several factors which may diminish or enhance its biological effect. The aim of the present work was to estimate the role of the liver in the process of renin inactivation.