Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is characterised by lung oedema due to increased permeability of the alveolar-capillary barrier and subsequent impairment of arterial oxygenation. Lung oedema and endothelial and epithelial injury are accompanied by an influx of neutrophils into the interstitium and alveolar space. Hence, the activation and recruitment of polymorphonuclear neutrophils (PMNs) are thought to play key roles in the progression of ALI/ARDS. Neutrophils, which have anti-microbial activity, are the first cells to be recruited to the site of inflammation. This review focuses on the mechanisms of neutrophil activity in patients with ALIs with respect to attachment, recruitment, adhesion, migration, activation, release of damage mediators, and apoptosis via PMNs.