Angiotensin-converting enzyme from rabbit lung particles will be characterized biochemically and investigated as a potential therapeutic target for the regulation of systemic blood pressure. Homogeneous enzyme solubilized and purified directly from pulmonary membranes and antibody to the pure enzyme will be used to establish: 1. The relationship of the enzyme to angiotensin-converting activities in (a) other organs, (b) serum and (c) the soluble fraction of the lung. 2. The identity of the metal bound to the enzyme and its role in catalysis. 3. The structure of the carbohydrate moiety of the enzyme, its relationship to known surface antigens and its role in catalysis. 4. The effect of participation in membrane structure upon the catalytic properties of the enzyme with angiotensin I and bradykinin as substrate. 5. The anatomic site of the enzyme. 6. The effect of antienzyme antibody on experimental hypertension.