We tested the insertion/deletion (I/D) polymorphism of the ACE gene in 119 hypertensive patients and in 109 normotensive controls by means of the polymerase chain reaction (PCR). The allele and genotype frequencies of the I/D polymorphism in the ACE gene are essentially identical in both groups, regardless of age or sex. The I/D polymorphism of the ACE gene is thus not implicated in Belgian hypertensive patients.