Flavonoids are phytochemicals that are widespread in the human diet. Despite limitations in their bioavailability,experimental and epidemiological data suggest health benefits of flavonoid consumption. Valid biomarkers of flavonoidintake may be useful for estimating exposure in a range of settings. However, to date, few useful flavonoid biomarkershave been identified. In this study, we used a metabolite profiling approach to examine the aromatic and phenolic profile ofplasma and urine of healthy men after oral consumption of 200 mg of the pure flavonoids, quercetin, (-)-epicatechin, andepigallocatechin gallate, which represent major flavonoid constituents in the diet. Following enzymatic hydrolysis, 71aromatic compounds were quantified in plasma and urine at 2 and 5 h, respectively, after flavonoid ingestion. Plasmaconcentrations of different aromatic compounds ranged widely, from 0.01 to 10 mmol/L, with variation among volunteers.None of the aromatic compounds was significantly elevated in plasma 2 h after consumption of either flavonoid comparedwith water placebo. This indicates that flavonoid-derived aromatic compounds are not responsible for the acutephysiological effects reported within 2 h in previous human intervention studies involving flavonoids or flavonoid-rich foodconsumption. These effects are more likely due to absorption of the intact flavonoid. Our urine analysis suggested thaturinary 4-ethylphenol, benzoic acid, and 4-ethylbenzoic acid may be potential biomarkers of quercetin intake and 1,3,5-trimethoxybenzene, 4-O-methylgallic acid, 3-O-methylgallic acid, and gallic acid may be potential markers ofepigallocatechin gallate intake. Potential biomarkers of (-)-epicatechin were not identified. These urinary biomarkersmay provide an accurate indication of flavonoid exposure. J. Nutr. 139: 2309–2314, 2009.