Acute lung injury (ALI) is a clinical syndrome in which patients develop severe and progressive pulmonary gas exchange defects and pulmonary mechanical dysfunction. The high morbidity and mortality (40%) associated with ALI provide a compelling need to identify clinical and/or biochemical parameters that robustly risk stratify patients for both accurate prognostication and clinical trial purposes. In this review, we will examine and critically evaluate studies pertaining to biochemical markers of mortality in ALI. These markers may not only serve as prognostic measures of disease, but in some cases, add to our overall understanding of the pathophysiology of ALI. © 2006 Elsevier B.V. All rights reserved.