Polymorphism in the angiotensin-converting enzyme (ACE) gene has been shown to correlate with circulating ACE concentrations, and also to be an independent risk factor for the development of myocardial infarction, particularly in men thought to be at low risk by standard criteria. We determined the genotypes of individuals with end-stage heart failure due to either ischaemic dilated cardiomyopathy (102) or idiopathic dilated cardiomyopathy (112) and compared these to organ donors with normally functioning hearts (79). Genotypes were determined by the polymerase chain reaction with oligonucleotide primers flanking the polymorphic region in intron 16 of the ACE gene to amplify template DNA isolated from patients. Compared with the DD frequency in the control population, the frequency of the ACE DD genotype was 48% higher in individuals with idiopathic dilated cardiomyopathy (p = 0.008) and 63% higher in subjects with ischaemic cardiomyopathy (p = 0.008), suggesting that an ACE gene variant may contribute to the pathogenesis of both types of cardiomyopathy.