The bioavailability and urinary excretion of three dietary flavonoids, quercetin, hesperetin and naringenin, were investigated. Ten healthy men were asked to consume a 'juice mix' containing equal amounts of the three flavonoids, and their urine and plasma samples were collected. The resulting mean plasma area under the curve (AUC)(0-48 h) and C(max) values for quercetin and hesperetin were similar, whereas the AUC(0-48 h) of naringenin and, thus, the relative bioavailability were higher after consumption of the same dose. The study consolidates a significantly lower urinary excretion of quercetin (1.5+/-1%) compared with hesperetin (14.2+/-9.1%) and naringenin (22.6+/-11.5%) and shows that this is not due to a lower bioavailability of quercetin, but rather reflects different clearance mechanisms.