1. To clarify the mechanism of the association between I/D polymorphism of the angiotensin-converting enzyme (ACE) gene and various cardiovascular disease, ACE mRNA levels in human atrial appendages were assessed in relation to the genotype of the ACE gene. 2. Angiotensin-converting enzyme mRNA levels were positively correlated with age and tended to show a positive correlation with mean pulmonary pressure (mPA). Multiple regression analysis indicated that age and mPA, but not the genotype of the ACE gene, were predictors of ACE mRNA levels in human atrial appendages. 3. The present study indicates that I/D polymorphism of the ACE gene is not simply reflected in ACE mRNA levels and that further study is needed to determine the mechanism of the association between this polymorphism and various cardiovascular diseases.