Polymorphisms of the angiotensin-converting enzyme (ACE) (insertion/deletion (I/D) in intron 16) and of the plasminogen activator inhibitor-1 (PAI-1) (promoter 4G/5G) genes have been linked with coronary heart disease (CHD) and/or myocardial infarction (MI). We studied the association of polymorphisms in these genes with CHD with linkage and association analyses in 118 families with premature and severe CHD and in 110 healthy controls. In linkage analysis there was no evidence for a linkage of the ACE or PAI-1 loci with CHD. However, in quantitative linkage analysis the ACE locus was linked with fasting glucose (P=0. 047) and fasting free fatty acid levels (P=0.029). In association analysis the ACE genotype frequencies of probands with CHD did not differ from those of healthy controls. Normoglycemic probands with MI and with the ACE polymorphism DD genotype had characteristics of the insulin resistance syndrome. They had higher levels of 1-h glucose (P=0.008) and 2-h free fatty acids (P=0.011) in an oral glucose tolerance test and higher levels of total (P=0.005) and very-low-density lipoprotein triglycerides (P=0.006) than probands with the ID or the II genotypes. The PAI-1 gene polymorphism was not associated with any of the variables of glucose or lipid metabolism. In conclusion, the ACE and PAI-1 gene polymorphisms are not linked with early-onset CHD. However, the ACE gene polymorphism is associated with features of the insulin resistance syndrome.