We investigated the role of the insertion (I)/deletion(D) polymorphism in the angiotensin I converting enzyme (ACE) gene in the cardiovascular diseases. First, we studied 520 patients who had undergone coronary angiography: including 220 patients with acute myocardial infarction, 98 patients with effort angina pectoris (> 75% stenosis), 83 patients with vasospastic angina and 119 controls with normal coronary artery. There was no difference in the frequency of ACE gene I/D allele or genotype II, ID and DD among the four groups. Second, we studied the correlation between ACE gene I/D polymorphism and the clinical characteristics in patients with essential hypertension. The distribution of I/D allele and genotype were similar in 140 essential hypertensives and 83 normal controls. In patients with DD genotype, age at onset of hypertension was lower and left ventricular mass index was greater than those in patients with ID and II, although blood pressure levels and the severity of damage to other organs-were similar in the three groups. Further, 66 patients with essential hypertension were classified into 35 salt-sensitive and 31 salt-resistant patients according to changes in mean blood pressure during a week of low salt diet followed by a week of high salt diet. The frequency of I allele was significantly higher in the salt-sensitive group than in the salt-resistant group. In conclusion, ACE gene I/D polymorphism is not associated with coronary artery diseases. In patients with essential hypertension, the D allele was associated with early onset and left ventricular hypertrophy, while I allele was associated with salt sensitivity.