Angiotensinogen is the only known substrate for the enzyme renin. Angiotensin II, the end product of the reaction, is an extremely potent vasoconstrictor and a major determinant of salt and water homeostasis. It is also a growth factor. Angiotensinogen has been identified as a non-inhibitory member of the serine proteinase inhibitor family. Although the most abundant source of plasma angiotensinogen is the liver, the use of Northern blotting and reverse transcriptase PCR techniques has confirmed angiotensinogen mRNA expression in a wide range of tissues, including the kidney, brain, vascular tissue, adrenal gland, placenta and leucocytes. The sequencing of the rat and human angiotensinogen genes has increased our understanding of this protein and its role in physiology and the pathogenesis of human disease. Early observations on the regulation of angiotensinogen are now explicable at the molecular level, with the identification of the core promoter, hormone and acute phase responsive elements and tissue-specific enhancers. The role of angiotensinogen in the aetiology of hypertensive disorders has been tested in transgenic animals, and in case-controlled genetic association and linkage studies. This review examines our current understanding of angiotensinogen, in the light of recent advances.