Red wine is a source of polyphenolic antioxidants, of which flavonols such as quercetin are representatives. Red wine might therefore prevent LDL oxidation and atherosclerosis. However, data on the bioavailability of flavonols from wine are lacking. Therefore, we compared the bioavailability of flavonols, especially quercetin, from red wine with that from the major dietary sources, yellow onions and black tea. Twelve healthy men consumed 750 mL red wine, 50 g fried onions or 375 mL of black tea, each for 4 d in random order. These supplements provided similar amounts of quercetin (14-16 mg). There was a washout period of 3 d between each period of supplementation. The plasma quercetin concentration after the consumption of wine was lower than that after onions (P < 0.05) and not different from that after tea. Urinary excretion of quercetin after wine did not differ from that after onions and was higher than that after tea (P < 0.05). We conclude that flavonols from red wine are absorbed. However, because one glass of red wine provides fewer available flavonols than one portion of onions or one glass of tea, red wine appears to be a poorer source of flavonols than these other two sources.