Angiotensin II is a primary reactive vasoconstrictor, the main stimulus for aldosterone release, and one of the causative factors of chronic hypertension. The active angiotensin II octapeptide is released via a tightly controlled series of prohormones and proteases. Normal human plasma angiotensin II levels are 10-30 pg/ml when measured at rest in the supine position; they increase on standing, exercise, dehydration, or sodium depletion. The unique, patented 'Immobilized Antigen' technology of this angiotensin II immunometric assay allows reliable detection of 1-2 pg/ml, or as little as 10% of the normal human plasma concentration.