New technologies in molecular biology and medicine have opened new avenues for the study of disease. As a result of this, the genetic basis of many diseases has been discovered and candidate genes that contribute to the underlying pathology have been identified. An important approach to test the function of these genes is the establishment of transgenic animal models. Candidate genes can be expressed in these animals to study their regulation in vivo. Furthermore, the pathophysiological consequences of the alteration in gene expression can be investigated in detail. Like many other diseases, primary hypertension is influenced by genetic factors. A number of candidate genes have been implicated in its pathogenesis, and current research efforts are directed toward testing these candidates. For this purpose, several transgenic animal models have been established. Most of this transgenic work has been carried out in mice, but recent efforts have focused on the development of transgenic rat models for hypertension, which may provide the better experimental system for the study of cardiovascular regulation.