Endothelial function is emerging as a surrogate marker for cardiovascular health and may be assessed using a non-invasive technique that employs increased flow and shear stress as a stimulus for brachial artery dilation. Flow-mediated dilation (FMD) is dependent on a healthy endothelium and the production and release of nitric oxide. In the presence of risk factors for CHD, for example chronic hyperlipidemia, FMD is attenuated. Acute hyperlipidemia, elicited by the ingestion of a high-fat meal has also been shown to impair FMD in healthy individuals for several hours. The resultant dysfunction may be due to increased levels of oxidative stress, suggesting that substances with antioxidant properties may protect against postprandial dysfunction. Estrogen has been shown to affect the endothelium causing the rapid release of nitric oxide. Estrogen may also have antioxidant properties. PURPOSE To test the hypothesis that postmenopausal women without hormone therapy would display impaired FMD following a high-fat meal and premenopausal women with endogenous estrogen, along with postmenopausal women with exogenous estrogen, would not display impaired FMD. METHODS Thirty healthy women were studied, 9 premenopausal, 10 postmenopausal with no hormone supplementation and 11 were postmenopausal taking hormone replacement therapy. FMD was measured following 4.5-mins of arterial occlusion including 1-minute of handgrip exercise after a 12-hour fast and again 3-hours after the ingestion of a high-fat meal (1018kcal, 56g of fat). RESULTS Following the high-fat meal FMD remained unaltered (9.39 ± 0.73 vs. 9.75 ± .0.64%, 8.71 ± 0.86 vs. 8.79 ± 0.79%, 9.80 ± 1.16 vs. 9.73 ± 1.06%, p<0.05) despite a significant increase in plasma TG levels (1.11 ± 0.2 vs. 1.91 ± 0.26mmol/L, 1.17 ± 0.15 vs. 1.86 ± 0.28mmol/L, 1.22 ± 0.24 vs. 1.78 ± 0.26mmol/L, p<0.0001 for premenopausal, postmenopausal and hormone replacement groups respectively). The high-fat meal also elicited a significant increase in insulin (9.45 ± 1.34 vs. 39.10 ± 11.32 ± μIU/ml, 8.89 ± 1.17 vs. 32.39 ± 3.17μIU/ml, 7.80 ± 0.81 vs. 32.63 vs. 4.77μIU/ml, p<0.0001). CONCLUSIONS Preserved FMD after a high-fat meal in this study may be explained by the use of healthy active women. Supported by NSERC Canada and the Heart and Stroke Foundation of ON, Canada