Acute biliary obstruction leads to periductal myofibroblasts and fibrosis, the origin of which is uncertain. Our study provides new information on this question in mice and humans. We show that bile duct obstruction induces a striking increase in cholangiocyte αvβ6 integrin and that expression of this integrin is directly linked to fibrogenesis through activation of transforming growth factor beta (TGF‐β). Administration of blocking antibody to αvβ6 significantly reduces the extent of acute fibrosis after bile duct ligation. Moreover, in β6‐null mice subjected to the injury, fibrosis is reduced by 50% relative to that seen in wild‐type mice, whereas inflammation occurs to the same extent. The data indicate that αvβ6, rather than inflammation, is linked to fibrogenesis. It is known that αvβ6 binds latent TGF‐β and that binding results in release of active TGFβ. Consistent with this, intracellular signaling from the TGFβ receptor is increased after bile duct ligation in wild‐type mice but not in β6^−/− mice, and a competitive inhibitor of the TGFβ receptor type II blocks fibrosis to the same extent as antibody to αvβ6. In a survey of human liver disease, expression of αvβ6 is increased in acute, but not chronic, biliary injury and is localized to cholangiocyte‐like cells. Conclusion: Cholangiocytes respond to acute bile duct obstruction with markedly increased expression of αvβ6 integrin, which is closely linked to periductal fibrogenesis. The findings provide a rationale for the use of inhibitors of αvβ6 integrin or TGFβ for down‐regulating fibrosis in the setting of acute or ongoing biliary injury. (HEPATOLOGY 2007.)