The aim of this study was to elucidate whether human renin gene restriction fragment length polymorphism (RFLP) is associated with essential hypertension. We sampled randomly 45 inpatients at our hospital and divided them into two groups according to a family history of essential hypertension, FH(-) and FH(+) groups. The FH(+) group was further divided into two subgroups based on the level of BP, FH(+) x HT(-) and FH(+) x HT(+) groups. The frequencies of renin gene RFLP patterns were compared among three groups: FH(-), FH(+) x HT(-) and FH(+) x HT(-). Among 18 restriction endonucleases tested, renin gene RFLPs were detected by three restriction endonucleases, Mbo I, Bg I and Hind III, digestion. There was a significant difference in the distribution of renin gene Mbo I genotypes among the three groups (chi 2 = 13.284, P < 0.01). The distribution of Mbo I genotypes in the FH(-) group was different from FH(+) x HT(-) group (chi 2 = 5.990, P < 0.05) and FH(+) x HT(+) group (chi = 9.210, P < 0.01), but there was no significant difference between the FH(+) x HT(-) and FH(+) x HT(+) groups. The distribution of renin gene Bgl I and Hind III genotypes were similar in the three groups, FH(-), FH(+) x HT(-) and FH(+) x HT(+). These results indicate that human renin gene Mbo I RFLP is significantly associated with a family history of essential hypertension.