Insertion/deletion (I/D) polymorphism of the angiotensin I converting enzyme (ACE) gene has been associated with ischemic heart disease and hypertension. The D allele reportedly correlates with myocardial infarction and it has been suggested that it may serve as the basis of population-based risk assessment. Similarly, determining whether there is an ACE allele pattern associated with hypertension could be useful in developing screening strategies. Previous reports have not shown consistent findings in Caucasian and Japanese population groups, some having a predominance of the I allele. Although African Americans have the highest prevalence of hypertension in the world, their ACE gene polymorphism frequencies have not been clearly defined. We studied the allele and genotype frequencies in this group, consisting of 133 essential hypertensive subjects, and compared their findings with those reported from normotensive African Americans and from other racial groups. The black patients had a different allele distribution than the other populations in that the D was more common than the I allele, occurring at a rate of 59.7%. The most common genotype was DD and it was present in 42.5% of the hypertensive subjects in contrast to the ID genotype which was the most commonly reported genotype in normotensive individuals. The genotype pattern (frequencies of II, ID, DD) was significantly different (p < 0.005, 2 df) from Japanese and Caucasian (Scotland and Australia) populations. There was no common allele or genotype distribution amongst these diverse hypertensive groups.(ABSTRACT TRUNCATED AT 250 WORDS)