Primary or "essential' hypertension is generally perceived to be a multifactorial or complex genetic trait. An individual's susceptibility to high blood pressure (BP) is influenced not only by the many genetic factors, which effect control through biochemical and physiological mechanisms, but also by environmental determinants. In a small proportion of human hypertensives the cause is a single genetic defect, exhibiting Mendelian characteristics. The vast heterogeneous majority, however, result from a multitude of contributing factors, making identification of the underlying etiology very difficult. We will briefly review a number of strategies which have helped to identify genetic factors involved in hypertension. These include the search for genetic defects in Mendelian forms of hypertension, intensive study of classical animal models such as the spontaneously hypertensive rat, and linkage analyses in animal models and hypertensive patients. We will then discuss the role which transgenesis can play in complementing and extending such analyses.