Significant correlation of body sodium and potassium with blood pressure (BP) may suggest a role for aldosterone in essential hypertension. In patients with this disease, the ratio of plasma renin to plasma aldosterone may be lower than in control subjects and plasma aldosterone levels may be more sensitive to angiotensin II (Ang II) infusion. Because essential hypertension is partly genetic, it is possible that altered control of aldosterone synthase gene expression or translation may be responsible. We compared the frequency of 2 linked polymorphisms, one in the steroidogenic factor-1 (SF-1) binding site and the other an intronic conversion (IC), in groups of hypertensive and normotensive subjects. In a larger population, the relationship of aldosterone excretion rate to these polymorphisms was also evaluated. In 138 hypertensive subjects, there was a highly significant excess of TT homozygosity (SF-1) over CC homozygosity compared with a group of individually matched normotensive control subjects. The T allele was significantly more frequent than the C allele in the hypertensive group compared with the control group. Similarly, there was a highly significant relative excess of the conversion allele over the "wild-type" allele and of conversion homozygosity over wild-type homozygosity in the hypertensive group compared with the control group. In 486 subjects sampled from the North Glasgow Monitoring of Trends and Determinants in Cardiovascular Disease (MONICA) population, SF-1 and IC genotypes were compared with tetrahydroaldosterone excretion rate. Subjects with the SF-1 genotypes TT or TC had significantly higher excretion rates than those with the CC genotype. The T allele was associated with higher excretion rates than the C allele. However, no significant differences were found in excretion rate between subjects of different IC genotype. Urinary aldosterone excretion rate may be a useful intermediate phenotype linking these genotypes to raised BP. However, no causal relationship has yet been established, and it is possible that the polymorphisms may be in linkage with other causative mutations.