The discovery of nitric oxide (NO) as a signalling and regulatory molecule and its subsequent detection in the exhaled breath has not only yielded new mechanistic insights but also diagnostic opportunities and therapeutic targets in several important medical conditions. In diseases involving chronic pulmonary inflammation such as asthma that affects millions worldwide, exhaled NO has achieved spectacular successes with patients currently owning handheld devices and monitoring inflammatory aspects of their conditions in their own homes. This has been facilitated by recognition by regulatory bodies, scientific and clinical societies and insurance companies. While characteristic changes in exhaled NO have also been observed in acute lung injury (ALI), the promise of exhaled NO as a surrogate biomarker of this life-threatening disease has not been achieved. In this work, we have analysed factors contributing to successes of exhaled NO in the asthma field and contrasted these on the ALI field. We provide a snapshot of current status of exhaled NO field in ALI and propose a framework for definite evaluation of exhaled NO as a clinically useful biomarker.