Protease activated receptor 2 (PAR2) is widely-distributed (lung, liver, kidney, etc.) and expressed by variety of cells (i.e. leukocytes, epithelial cells, endothelial cells, and fibroblast). PAR2 may participate in many pathological processes, such as, inflammation, injury, as well as fibrosis. Therefore, in this study, we tested whether PAR2 would exert a role in acid-induced acute lung injury, E. coli pneumonia, bleomycin-induced acute lung injury and fibrosis. Acid, E. coli, or bleomycin were intratracheally instilled into the lungs of both wildtype and PAR2 knockout mice to detect differences in pulmonary edema, lung vascular permeability, lung fibrosis, and other parameters. Knockout of PAR2 did not affect the extent of pulmonary edema and lung vascular permeability in acid-induced acute lung injury. Also, both activation of PAR2 in the airspaces of the lung and deletion of PAR2 did not alter the magnitude of pulmonary edema and lung vascular permeability in E. coli pneumonia. Finally, PAR2 deficiency did not affect the severity of lung inflammation and lung fibrosis in bleomycin-induced acute lung injury and lung fibrosis models. Thus, PAR2 does not appear to play a critical role in the pathogeneses of experimental acid-induced acute lung injury, E. coli pneumonia, and bleomycin-induced acute lung injury and pulmonary fibrosis in mice. Anat Rec, 2009. © 2009 Wiley-Liss, Inc.