There is now considerable evidence for an increased oxidant burden in patients with chronic obstructive pulmonary disease (COPD). Oxidative stress is a critical feature in the pathogenesis of COPD, since it results in inactivation of antiproteinases, airspace epithelial injury, MUCUS HYPERSECRETION, increased influx of neutrophils into the lungs, transcription factor activation and gene expression of pro-inflammatory mediators. Antioxidants should therefore not only protect against the direct injurious effects of oxidants, but also may fundamentally alter the inflammatory events which have a central role in the pathogenesis of COPD.