Aldosterone synthase (CYP11B2) is a key enzyme in the biosynthesis of aldosterone. Recently, a polymorphism in the 5'-flanking region of the CYP11B2 gene [T(-344)C] has been reported to be associated with blood pressure and plasma aldosterone levels. We investigated the association between this polymorphism and hypertension in a large population-based sample of 4,000 Japanese. The genotype distribution in hypertensive subjects (n=1,535) was compared to that in normotensive subjects (n=2,514). In subjects not receiving antihypertensive medication, the influence of the genotype on blood pressure values adjusted for clinical covariates was analyzed. All analyses were performed separately for men and women. The genotype distribution did not differ between hypertensive and normotensive subjects in either men (frequency of C allele: 30.3% vs. 31.4%, p=0.48) or women (31.5% vs. 31.7%, p=0.93). There were no significant differences in systolic blood pressure, diastolic blood pressure, or pulse pressure among the three genotypes in either men or women who had not received hypertensive medication. Our data suggest that the T(-344)C polymorphism of CYP11B2 is unlikely to influence blood pressure status in the Japanese population.