In our previous study using cell lines overexpressing ABCG2, we showed that curcumin inhibited the activity of ABCG2 in in vitro assays (13). The objective of the present study was to demonstrate the inhibitory activity of curcumin on ABCG2 function under normal physiological conditions in an in vivo system. To demonstrate this in a model close to the in vivo situation, we used freshly isolated, functionally active rat brain capillaries. Isolated brain capillaries are an estab- lished ex vivo model for the blood–brain barrier, a tissue well-