1. The development of the transgenic technology for the rat allowed the evaluation of gene functions in the cardiovascular system in vivo. New insights have been gained particularly in the functions of the renin-angiotensin system (RAS), as most transgenic rat models established so far carry genes of this system. 2. TGR(mREN2)27 is a rat harbouring the mouse Ren-2 gene and exhibiting fulminant hypertension. The plasma RAS in this animal is down-regulated; however, the tissue-specific production of angiotensin II is activated (e.g. in the adrenal gland, the brain and the vessel wall). The physiological consequences of this activation, which finally leads to hypertension, can be studied in TGR(mREN2)27, rendering it a valuable tool in the functional analysis of tissue RAS. 3. TGR(hREN) and TGR(hAOGEN) carry the human genes for renin and angiotensinogen, respectively. In these animals the species-specific interaction of the two proteins and the expression pattern of the genes can be studied. Furthermore, these animals can be used to test renin-inhibitory drugs for use in antihypertensive therapy. 4. Further refinement of transgenic methodology (e.g. by the development of gene targeting in rats), should enhance our understanding of the functions of the RAS in cardiovascular regulation.