Deletion polymorphism in intron 16 of the angiotensin I-converting enzyme(ACE) gene has been found to be associated with a risk of essential hypertension in some black American populations. Among some caucasian populations, however, this same polymorphism has been found to be associated with an increased risk for myocardial infarction. In an on-going family study in black Americans, we compared the frequency of the ACE deletion polymorphism in 21 hypertensive probands with 28 normotensive healthy controls drawn from the same clinic. The frequency of the deletion allele in hypertensive probands was significantly higher than in normotensive controls, 0.738 versus 0.571 with p<0.01. This suggests that polymorphism in or near the ACE gene might contribute to an increased risk of essential hypertension in blacks.