The use of clinical, physiologic, and laboratory parameters in the prediction or early detection of ARDS has been reviewed. From both a clinical and research standpoint, the ability to identify patients at risk is extremely important. The selection of patients according to predisposing clinical events has been the most successful thus far. The use of physiologic variables and gauges of injury severity have been of limited value, particularly for assessing ARDS risk in the individual patient. Only a handful of the proposed mediators or markers of acute lung injury have been studied prospectively in patients at risk. Of these, factor VIII antigen, lactoferrin, and phospholipase A2 appear the most promising as laboratory tests for selecting patients at risk. In the future it may be possible by using sophisticated statistical analysis techniques to combine important clinical, physiologic, and laboratory information into a numerical ARDS risk index, essentially assigning a probability of ARDS in individual patients.