Blood pressure is a quantitative multifactorial trait with both environmental and genetic determinants, with essential hypertension simply representing one extreme of the blood pressure distribution. While much is known about environmental factors that predispose to the development of hypertension, the nature of the genetic factors that increase such susceptibility remain virtually unknown. However, with advances in molecular techniques, several loci that influence blood pressure in rodents have been identified and recently in two selected sets of human hypertensives, a molecular variant at the angiotensinogen locus has been linked to the tendency to hypertension. It is likely that in the next few years several genetic determinants of blood pressure variability in humans will be identified. Such information will not only increase our understanding of the pathophysiology of hypertension and identify novel treatments but may permit preventative and therapeutic measures to be targetted more specifically than at present.