Insertion/deletion (I/D) polymorphism of angiotensin-I-converting enzyme (ACE) gene was studied by use of the polymerase chain reaction in 168 normal subjects living in Moscow region and in 70 patients: 38 with essential hypertension (EH), 9 of which survived myocardial infarction at young age, 13 with hypertrophic cardiomyopathy (HCMP) and 19 with myocardial infarction (MI). Left ventricular hypertrophy (LVH) was detected in 24 of 38 EH patients. There was a highly significant increase in the frequency of the ID genotype in EH patients compared to the controls (62.4% versus 32.7%, P < 0.01). There was a relevant decrease in the frequency of the DD genotype in EH patients in comparison with the control (20.8% versus 47.6%, P < 0.05). These results strongly suggest that the ACE gene is associated with EH. No significant differences in both allele and genotype frequencies of the ACE gene were revealed in two groups of patients with MI and with HCMP compared to the controls. Thus, no relations between the ACE gene and these disorders were observed. In hypertensives with MI the II genotype was not detected and the frequency of both D allele and DD genotype was sufficiently increased compared to normotensive patients with MI. Thus, the DD genotype in hypertensives may be a risk factor for MI. The frequency of the DD genotype was significantly increased in hypertensive patients with LVH compared to the uncomplicated hypertension (37.5% versus 7.1%, P < 0.05). Therefore, this genotype is associated with LVH in hypertensive subjects.