The spontaneously hypertensive rat (SHR) is the most widely used animal model of human essential hypertension. In the SHR strain, as in humans, the high blood pressure is determined multifactorially. Analysis of genetically segregating populations, derived from SHR and normotensive inbred strains, enabled localization of quantitative trait loci (QTLs) responsible for blood pressure regulation on several rat chromosomes. Analysis of specialized strains, congenic and recombinant inbred (RI) strains, helped to analyze some of these mapping results in detail: (1) analysis of congenic strains provided definitive evidence for the presence of blood pressure regulatory genes on chromosomes 8 and 13 and will enable mapping of responsible genes to limited segments of differential chromosomes, (2) the RI strains were shown to be especially useful for genome scanning studies of complex traits and for correlation analysis of blood pressure and other risk factors of cardiovascular disease such as cardiac hypertrophy, dyslipidemia, and insulin resistance.