Induced sputum 8-iso-prostaglandin F(2alpha) (PGF(2alpha)) concentrations may be a useful marker of oxidative stress in airways disease. This study examines oxidative stress (measured by 8-iso-PGF(2alpha)) in airway disease according to disease type (asthma and bronchiectasis), disease activity (stable and acute asthma), and disease pattern (intermittent, mild, moderate, and severe persistent asthma). We compared subjects with stable asthma (n = 71) and bronchiectasis (n = 23) with healthy control subjects (n = 29). Another group of patients with asthma (n = 39) were assessed during and after acute exacerbation. Induced sputum 8-iso-PGF(2alpha) concentrations were validated and found to be elevated in subjects with stable asthma and bronchiectasis versus control subjects (median [interquartile range] 216 [103-389] and 698 [264-1,613] ng/L vs. 123 [41-290] ng/L, p < 0.001) and increased as clinical asthma pattern worsened (intermittent 115 [42-153], mild persistent 116 [89-229] ng/L, moderate persistent 183 [110-317] ng/L, severe persistent 387 [102-587] ng/L; p = 0.010). Sputum 8-iso-PGF(2alpha) concentrations were elevated during acute asthma and decreased with recovery (458 [227-950] ng/L vs. 214 [148-304] ng/L, p = 0.0002). We conclude that 8-iso-PGF(2alpha) is involved in the pathophysiology of inflammatory airway diseases, being related to disease type, pattern, and activity. Analysis of 8-iso-PGF(2alpha) concentrations in induced sputum provides a useful tool for monitoring oxidative stress and investigating strategies aimed at reducing oxidative stress in airways disease.