Obesity is associated with an increased risk of atherosclerotic coronary artery disease. Cytokines and oxygen-centered free radicals implicated in insulin resistance stimulate adipocyte and endothelial production of plasminogen activator inhibitor type-1 (PAI-1), the primary physiologic inhibitor of fibrinolysis, in vitro. In obese hyperinsulinemic animal models simulating insulin resistance, plasma PAI-1 activity is increased. As the cardiovascular risk profile in specific populations may differ, endogenous fibrinolysis in lean and obese subjects was characterized and the mechanisms underlying differences were identified. Obese subjects (body mass index > 26) exhibited increased blood levels of PAI-1 antigen compared with corresponding values in lean controls. Blood t-PA antigen differed as well, yet basal endogenous fibrinolytic activity was decreased because of the high PAI-1 activity. The increased PAI-1 level was associated with increased levels of immunoreactive insulin (IRI). In diabetic subjects, coronary atherectomy specimens exhibited strong positive PAI1 immunostaining, suggesting that in the diabetic vascular wall, intramural fibrinolytic activity is diminished. Using the oral glucose tolerance test, patients with significant stenosis confirmed by coronary angiography exhibited increased ∑IRI, ∑BS, ∑IRI/∑BS, and IRI at 120 min compared to subjects without significant stenosis. IRI at 120 min was closely correlated with the severity of coronary artery disease. These results indicate that adipocyte overproduction of PAI-1 by insulin induces decreased endogenous fibrinolytic activity and contributes to the accelerated coronary macroangiopathy in hyperinsulinemic obese subjects with insulin resistance.