Activated neutrophils and their histotoxic products, particularly human neutrophil elastase (HNE), have been specifically implicated in the pathogenesis of ALI/ARDS, and there is considerable clinical interest in new drugs in this area. However, there is currently no way of rapidly determining whether new therapeutic candidates are exerting their predicted effects in situ in the human lung prior to embarking upon major clinical trials. Such a solution would inevitably accelerate the pathway of new drugs to clinical application.