JRAAS 2001;2:205-10 Introduction The renin-angiotensin system (RAS) was initially identified as a circulating humoral system with the effector peptide,angiotensin II (Ang II),generated by an enzymatic cascade. Angiotensinogen, which is synthesised in the liver, is cleaved by renin,a product of the juxtaglomerular cells of the kidney, to form angiotensin I (Ang I), which in turn is cleaved by angiotensin-converting enzyme (ACE) to form Ang II. ACE is membrane-bound and predominates on the endothelial cells of all vascular beds.Apart from the production of Ang II in plasma,Ang II, renin and ACE have all been described in tissues such as the brain, kidney, adrenal, vasculature, heart and ovaries. This suggests a separate and distinct RAS in these tissues and implies endocrine,paracrine and autocrine roles for Ang II. A variety of other angiotensin peptides are also produced,although their activities have only recently received attention.