An association study of the polymorphism of the angiotensinogen gene, consisting of T-->C transition at nucleotide 704 in exon 2, with essential hypertension in the Japanese population was performed by restriction fragment length polymorphism (RFLP). The allele which contained the Tth 111-I restriction site in the presence of C transition was designated 'a' and the allele that lacked restriction site was designated 'A'. The frequency of aa genotype in our normotensive group was higher than the previously reported values in Caucasians. In spite of the high frequency of the aa genotype in Japanese, the aa genotype was significantly more frequent in 108 hypertensives than in 104 normotensive subjects compared with the two other genotypes (P = 0.009). These results suggested that this molecular variant of the angiotensinogen gene may be a preserved inherited predisposition for essential hypertension in various ethnic groups, including Caucasians and Japanese.