A polymorphism characterized by the insertion or deletion of a 287-bp Alu repeat sequence in intron 16 of the angiotensin-converting enzyme gene determines about half the serum angiotensin-converting enzyme level variability among individuals. The deletion polymorphism is associated with higher levels of angiotensin-converting enzyme and perhaps with a greater risk of cardiovascular diseases. The relative frequency of this genetic polymorphism in different ethnic groups is not known. The objective of this study was to compare the frequency of angiotensin-converting enzyme gene insertion/deletion polymorphism in different ethnic groups. Angiotensin-converting enzyme genotype was determined in middle-aged healthy hospital workers of three different ethnic origins (African Americans, whites, and Indians). There were 142 African Americans, 136 Indians, and 82 whites. The distribution of the deletion-deletion, insertion-deletion, and insertion-insertion genotypes in African Americans (29%, 60%, and 11%, respectively), Indians (19%, 50%, and 31%, respectively) and whites (29%, 40%, and 31%, respectively) was significantly different (p = < 0.005). The frequency of the deletion allele among African Americans, Indians, and whites (0.59, 0.49, and 0.44, respectively) was also significantly different (p=0.05). African Americans had the highest frequency of deletion allele and the lowest frequency of the insertion-insertion genotype among the three groups. The frequency of the deletion polymorphism of the angiotensin-converting enzyme gene is different among African Americans, whites, and Indians. This may be important in relation to the high risk of cardiovascular morbidity and mortality in African Americans and may be relevant in explaining differences in cardiovascular diseases in different populations. This finding also emphasizes the importance of studying angiotensin-converting enzyme gene polymorphism in genetically homogenous populations. Because of the small size of this study, however, these findings need further confirmation.