We investigated the association between a dinucleotide (cytosine-adenine; CA) repeat polymorphism located in the flanking region of the human estrogen receptor beta (ESR2) gene and systemic blood pressure in 187 healthy postmenopausal Japanese women. The genotype was classified as "A" through "O" according to the number of these repeats from 18 to 32. When we separated the subjects into two groups-- bearing at least one "I" allele (26 CA repeats) and those who did not--we found that the former subjects had significantly higher systolic blood pressure than the latter (mean +/- SD, 146.0 +/- 25.0 vs 136.6 +/- 23.4; P = 0.032). These data suggest that genetic variation at the ESR2 locus may be associated with some determinants of blood pressure, and that there is a possible involvement of this polymorphism in causing hypertension in Japanese women.