Copyright © 2014 by the American Thoracic Society. Acute lung injury in response to mustard gas (sulfur mustard [SM]) inhalation results in formation of fibrin casts, which obstruct the airway. The objective of this study was to identify fibrinolytic pathways that could be contributing to the persistence of airway casts afterSMexposure. Rats were exposed to theSManalog, 2-chloroethyl ethyl sulfide, via nose-only aerosol inhalation. At 4 and 18 hours after exposure, animals were killed and airway-capillary leak estimated by measuring bronchoalveolar lavage fluid (BALF) protein and IgM content. The fibrin clot-degrading and plasminogenactivating capabilities of BALF were also assessed by activity assays, whereas Western blotting was used to determine the presence and activities of plasminogen activator inhibitor-1, thrombin activatable fibrinolytic inhibitor and α2-antiplasmin. Measurement of tissuespecific steady-state mRNA levels was also conducted for each fibrinolytic inhibitor to assess whether its synthesis occurs in lung or at extrapulmonary sites. The results of this study demonstrate that fibrin-degrading and plasminogen-activating capabilities of the airways become impaired during the onset of 2-chloroethyl ethyl sulfide-induced vascular leak. Findings of functionally active reservoirs of plasminogen activator inhibitor-1, thrombin activatable fibrinolysis inhibitor, and α2-antiplasmin in BALF indicate that airway fibrinolysis is inhibited at multiple levels in response to SM.