Endothelin-1 is a potent vasoconstrictor that has also mitogenic properties, stimulating the synthesis and secretion of several vasoactive molecules. There is much evidence to suggest that endothelin-1 might be involved in the pathogenesis of hypertension, atherosclerosis, and ischemic heart disease. Endothelin-1 exerts its effects through at least two receptors, ET(A) and ET(B), which are encoded by different genes and have separate tissue distributions and biologic properties. The objective of this study was to identify polymorphisms of the ET(A) and ET(B) receptor genes and to study their association with myocardial infarction (MI) and blood pressure. The coding regions and 1.3 kb upstream of the ET(A) and ET(B) receptor genes were explored by polymerase chain reaction/single strand conformation polymorphism. Six polymorphisms were found in the ET(A) receptor gene and three in the ET(B) receptor gene. Most of these polymorphisms were frequent. Associations between the detected polymorphisms, blood pressure, and MI were examined in the ECTIM study, a multicenter study comparing 652 patients having survived an MI and 773 controls from Belfast (Northern Ireland) and France. Alleles at the different polymorphic sites were similarly distributed in patients with MI and controls. Allele frequencies were similar in both countries, except for the ET(A)/-231 G allele, which appeared more frequently in France than in Belfast (P < .01). The mean systolic and diastolic blood pressure levels did not significantly differ between genotypes. However, a C/T substitution located in the nontranslated part of exon 8 of the ET(A) receptor gene (ET(A)/EX8nt1363) was associated with pulse pressure (P < .005). These results do not support an involvement of the endothelin receptor genes in a predisposition to MI or the determination of blood pressure levels, but suggest that a polymorphism of the ET(A) receptor gene might influence the pulse pressure. This result will have to be confirmed in other studies.