Angiotensin-converting enzyme (ACE) levels and ACE gene polymorphisms have been related with hypertension but with contradictory results between populations. We have investigated the association among the allelic distribution of the insertion-deletion (I/D) polymorphism of the ACE gene, identified by polymerase chain reaction (PCR), serum ACE activity determined by spectrophotometry, and the blood pressure (BP), in a Mediterranean population in the southwest of Europe. A total of 1322 randomised individuals were analysed, and a comparative study was conducted analysing 205 individuals from the group with highest BP (fifth quintyl) and 196 from the group with lowest BP (first quintyl). In addition we have studied the frequencies of alleles in separated groups of women and men. We conclude that in this population there is no association between I/D polymorphism and hypertension. However, we have found a statistically significant association between the presence of the D allele in the genotypes and an elevation of serum ACE activity.