Angiotensin is formed from a precursor, angiotensinogen, which is produced by the liver and found in the alpha-globulin fraction of plasma. The lowering of blood pressure is a stimulus to secretion of renin by the kidney into the blood. Renin cleaves from angiotensinogen a terminal decapeptide, angiotensin I. This is further altered by the enzymatic removal of a dipeptide to form angiotensin II.

The human angiotensinogen molecule has a molecular weight of about 50,000 Da. The angiotensin I decapeptide is located in its N-terminal part. The human angiotensinogen gene is assigned to 1q4 in the same region as the renin gene and contains 5 exons.