In 1898, Tiegersted and Bergman described that extracts of kidney induced an increase of blood pressure when injected into rabbits. They also named the detected biologic activity renin. The cleavage of angiotensinogen yields angiotensin I which is further processed by angiotensin converting enzyme to angiotensin II. The crucial role of renin in controlling blood pressure via the angiotensinogen cleavage and consequently its role in hypertension and congestive heart failure urged a broad research concerning this enzyme. Several mechanisms were suggested to be involved in the renin release from epithelioid cells. They include exocytosis, a lysosome-dependent mode of excretion and the intracytoplasmic solubilization of the stored secretory product. The treatment of hypertension represents the major goal of the investigations of the specific inhibition of renin activity. The use of monoclonal antibodies raised against human renin is a useful approach in physiological studies.