Transgenic animals are used to study the function, regulation and in vivo expression of genes. The effects of the genes of the renin-angiotensin system on blood pressure regulation and hypertension were invested in transgenic rats. The role of the renin-angiotensin system in the development of the cardiovascular hypertrophy or hypertensive renal damage was analysed, as well as its interaction with other hormonal systems, i.e., adrenal steroids. The development of a transgenic rat strain carrying the mouse REN-2 gene has provided a new model of hypertension with systolic blood pressure values of 200 mmHg. This model is characterised by low active plasma renin, hyperproreninaemia and high expression of renin in the adrenal gland and other external tissues. Transgenic rats with the human components of the renin-angiotensin system expressed the human renin and angiotensinogen proteins which interacted species-specifically in transgenic rats. These transgenic models demonstrate the feasibility of studying the function of candidate hypertension genes in transgenic animals. In the future, further refinements in transgene construction, mutation, and modification can be tested in such transgenic animal models.