We have shown that the integrin αvβ6 activates latent TGF-β in the lungs and skin. We show here that mice lacking this integrin are completely protected from pulmonary edema in a model of bleomycin-induced acute lung injury (ALI). Pharmacologic inhibition of TGF-β also protected wild-type mice from pulmonary edema induced by bleomycin or Escherichia coli endotoxin. TGF-β directly increased alveolar epithelial permeability in vitro by a mechanism that involved depletion of intracellular glutathione. These data suggest that integrin-mediated local activation of TGF-β is critical to the development of pulmonary edema in ALI and that blocking TGF-β or its activation could be effective treatments for this currently untreatable disorder.