In the presence of red wine or grape juice, low-density lipoprotein was significantly resistant to oxidation; the biological activity of flavonoids, but not ethanol or nonflavonoid phenolic compounds, appeared to contribute to the antioxidant properties of red wine and grape juice. A significant antioxidant activity was also confirmed in low-density lipoprotein from humans after ingesting red wine but not grape juice, suggesting that flavonoids in red wine can be absorbed from the intestine more efficiently than those in grape juice.