The bioactivities, dietary sources, bioavailability, metabolism, and epidemiology of 3 flavonoids, quercetin, hesperetin, and naringenin, are reviewed. The use of their plasma concentrations as biomarkers of dietary intake is also discussed. The compounds were chosen because of their significant dietary intakes and promising bioactivities, and in the case of quercetin, because epidemiological studies suggest protection against cardiovascular disease. (C) 2004 Elsevier Inc. All rights reserved.