Anthocyanins are secondary metabolites from the flavonoid family, frequently found in fruits and vegetables. They have been shown to possess beneficial health effects and various in vitro assays have highlighted their powerful antioxidant capacity. However, little is known about their metabolism after digestion and their antioxidant potency in vivo. The aim of this work was to evaluate anthocyanin bioavailability and to determine the impact of an anthocyanin-rich diet on plasma antioxidant status in rats. Animals were fed for 8 days with a vitamin E-deficient diet supplemented with a bilberry (Vaccinium myrtillus L.) anthocyanin extract providing daily 1.43 mmol anthocyanins kg(-1) body weight. An anthocyanin-enriched diet significantly enhanced the plasma antioxidant capacity compared with a control diet (P < 0.0001). Moreover, anthocyanins were recovered in urine in the intact glycosidic forms in addition to unknown metabolites. Urinary excretion of bilberry anthocyanins and their metabolites was 0.71 +/- 0.08 mu mol per 24 h (ie 0.22% of the ingested dose). Anthocyanins and their corresponding aglycones were detected in caecal contents. After a single oral administration of the bilberry extract, native anthocyanins quickly (30 min) appeared in plasma. Hence, in spite of a low bioavailability, bilberry anthocyanin extract consumption has a positive effect on plasma antioxidant capacity.