The genetic basis of essential hypertension is still uncertain. Because renin is thought to be a candidate gene for essential hypertension, a prospective study was conducted to compare the frequency of renin gene HindIII restriction fragment length polymorphism (RFLP) in normotensive and hypertensive subjects without (HTG-) and with a genetic predisposition to essential hypertension (HTG+). The frequency of the 9.0-kb fragment was significantly (p < 0.05) higher in the HTG+ group than in the normotensive and HTG- groups. An association between renin RFLP and hypertension in man was shown for the first time. It is suggested that a gene for blood pressure regulation has been localized to a part of the genome close to, or identical to, the renin locus.