Nitric oxide (NO) regulates endothelial function and is believed to prevent atherogenesis. In endothelial cells, endothelial nitric oxide synthase (eNOS) is expressed constitutively, and regulates NO synthesis. A mutation of the eNOS gene has been associated with the development of coronary artery disease (CAD). The development of CAD is also influenced by insulin resistance, and recent studies suggest that NO might affect cellular insulin activity. We investigated the association between eNOS polymorphisms and insulin resistance in patients with CAD. We screened 45 patients with a history of myocardial infarction (MI), angina pectoris (AP), or coronary spasm. Genotypes were determined by polymerase chain reaction-restriction fragment-length polymorphism analysis. We examined two polymorphisms of the eNOS gene (The T(-786)-->C variant and the missense Glu298Asp variant). Insulin resistance was measured by determining the plasma immunoreactive insulin concentration at the 120 min time point (IRI 120) of a 75 g oral glucose tolerance test. The IRI 120 of the T(-786)-->C variant group was higher than that for the control group (p<0.05). This finding demonstrates that the T(-786)-->C mutation in the eNOS gene decreases insulin sensitivity.