Recent findings have increased our understanding of the role of the renin-angiotensin system in cardiovascular diseases. This was possible by the progress made in molecular biology and the import of this methodology into cardiovascular research by several groups in the past few years. Studies by these groups accumulated evidence especially for the existence and physiological importance of organ-based renin-angiotensin systems and their involvement in the pathogenesis of hypertension and the accompanying disorders of the heart, the kidney, and the vessels. This Review will focus mainly on the relevance of the local renin-angiotensin systems for cardiovascular diseases and the value of transgenic animals as models to analyse these systems (Hypertens Res 1994; 17: 1-16).