In addition to preserving homeostasis and contributing to immunity, platelets may exhibit a dysregulated state in acute respiratory distress syndrome (ARDS), and potentially exacerbate lung injury. Although thrombocytopenia has been associated with increased mortality in ARDS and particularly in H1N1 influenza-infected patients, analysis of quantitative changes in platelet activation levels in ARDS, and how these may differ between the various etiologies of ARDS remains limited.