Oxidative stress contributes to airway inflammation and exhaled hydrogen peroxide (H2O2) is elevated in patients with bronchiectasis. However, the precise role of H2O2 in the pathophysiology of inflammatory processes remains unclear. We determined the concentration of exhaled H2O2 in 30 patients with documented bronchiectasis (24 male, mean age 39 ± 2.5 yrs, FEV1 69 ± 4 % pred) and studied the relation between levels of exhaled H2O2 and extent of the disease by high resolution computed tomographic scan (HRCT), spirometry and cellular population obtained from induced sputum. Additionally steroid treated patients were compared with steroid naοve. Exhaled H2O2 levels were significantly elevated in patients with bronchiectasis compared to 15 normal subjects (12 men, age 34 ± 4 yrs, FEV1 95 ± 3 % pred) (1.1 ± 0.1 μM vs. 0.3 ± 0.04 μM, p<0.0001). There was a significant positive correlation between H2O2, percentage of neutrophils in induced sputum and extent of the disease, as defined by the HRCT scoring scale system (r=0.9, p<0.0001 and r=0.66 p<0.0001, respectively). A significant negative correlation was found between H2O2 and FEV1 % pred (r=-0.42, p<0.05). Patients who were on inhaled steroids had similar values with steroid naοve (1.15 ± 0.15 μM vs. 1.02 ± 0.1 μM, p=0.12). In conclusion, patients with bronchiectasis in stable condition showed increased levels of exhaled H2O2. Hydrogen peroxide levels could be an index of the inflammation, obstruction and extent of the disease. Pneumon 2000, 13 (2): 144-153