Remnant lipoproteins (RLPs) accumulate in type III hyperlipoproteinemia, a condition associated with significant cardiovascular morbidity, The effect of RLPs on fibrinolysis is unknown. Our aim was to study the effect of RLPs on endothelial expression of plasminogen activator inhibitor-1 (PAI-1), After 24-11 culture of human aortic endothelial cells with RLPs at concentrations of 0 (control), 0.038, or 0.076 mg triglyceride/ mt, postculture PAI-1 antigen concentrations were: 870 +/- 80, 1983 +/- 183 (P = 0.005), and 3551 +/- 177 ng/mL (P < 0.001), respectively. Furthermore, after 24-h incubation of endothelial cells with RLPs (0 or 0.076 mg triglyceride/mL), PAI-1 activity increased from 0.667 +/- 0.144 to 1.268 +/- 0.198 U/mL, respectively (P = 0.008) and endothelial PAI-1 mRNA increased to 2.7 +/- 0.66 that of control (P = 0,048), In conclusion, RLPs from patients with type III hyperlipoproteinemia induce endothelial cell PAI-1 expression, which may contribute to a prothrombotic state.