Oxidative stress is an important trait in the pathogenesis of chronic obstructive pulmonary disease (COPD). Consequently, targeting oxidative stress is likely to be beneficial as a treatment in COPD. Glutathione (GSH) is an intracellular antioxidant that protects against a variety of different antioxidant species. The increase of lung GSH in COPD is an attempt to counter excess oxidant production but it is inadequate during exacerbations due to the excessive production of ROS. N-acetyl-l-cysteine (NAC) acts as a precursor for the substrate cysteine in synthesis of GSH and also as a mucolytic and anti-inflammatory agent. NAC prevents COPD exacerbations at high dosage (≥1200 mg daily), while a regular treatment with 600 mg daily is enough in chronic bronchitis. Nonetheless, we must still establish whether the level of bronchial obstruction may influence its effects, the effect of high-dose NAC in Caucasian patients with COPD, and the role of NAC in the escalation and de-escalation of therapy in COPD.