The insertion/deletion DNA polymorphism of the gene coding human angiotensin converting enzyme (ACE) was examined in 109 patients with coronary artery disease (CAD) and 93 non-coronary subjects (NCS) living in a northern part of Japan. The presence of risk factors including age, hypertension, hypercholesterolemia, tobacco use, diabetes mellitus and hyperuricemia were also examined. An insertion (I) / deletion (D) polymorphism of the ACE gene was determined by the polymerase chain reaction with oligonucleotide primers encompassing the polymorphic region in intron 16. The template DNA was isolated from peripheral blood leukocytes of patients. The frequency of the D-allele in NCS was 0.27, significantly lower than that reported in Caucasians or in Japanese living in the Osaka area. The frequency of the D-allele in patients with myocardial infarction (MI) and angina pectoris was 0.39 and was higher than that in NCS. The frequencies of genotypes DD, ID, and II were 17.8, 43.3 and 38.9%, respectively, in CAD except in young patients (below 40 years of age) with MI and AP groups, and 6.5, 40.9 and 52.7%, respectively in NCS (p < 0.05 between CAD and NCS). Young MI showed similar frequencies in ACE gene polymorphisms to those in NCS, a pattern which differed from that seen in subjects with CAD (p < 0.05). The numbers of risk factors did not alter the frequency of ACE gene genotype among patients with CAD, however, in normotensives, the odds ratio of DD-genotype was significantly increased to 3.4. Accordingly, ACE gene polymorphism may be associated with morbidity from CAD in Japanese living in northern Japan as has been noted in Caucasians, despite the lower frequencies of the D-allele in the Japanese population.