OBJECTIVE : To localize quantitative trait loci (QTL) in an animal model that is potentially relevant to human hypertension. DESIGN AND METHODS : Four congenic strains have been constructed by replacing various segments of the Dahl salt-sensitive (S) rat by those of the Lewis (LEW) rat. A marker-assisted approach was employed to facilitate this process. When these congenic strains were established, their blood pressures (BPs) were measured by telemetry and compared with that of the S rat. Moreover, a search was conducted to find possible intermediate phenotypes linking the BP effects of the QTL and other physiological traits. RESULTS : Two BP QTL, designated as QTL1 and QTL2, have been mapped to the regions of 4.2 centiMorgans (cM) and less than 12.1 cM respectively on rat chromosome 10. The effects of both QTL correlate with cardiac, left ventricular and aortic hypertrophy. The effect of QTL1 is also associated with renal hypertrophy. CONCLUSION : The current study proved that multiple QTL exist in the region of Dahl rat chromosome 10. The identification of these QTL may help unravel the mechanisms underlying the pathogenesis of certain QTL in humans.