Ethane is a product of lipid peroxidation and can be measured in the exhaled air as an index of oxidative stress. Oxidant/antioxidant imbalance is important in the pathogenesis of chronic obstructive pulmonary disease (COPD). Therefore, we measured exhaled ethane in 22 patients with COPD (mean age +/- SEM, 59 +/- 8 yr; 19 male) and compared it with other noninvasive markers of oxidative stress and inflammation such as carbon monoxide (CO), measured electrochemically, and nitric oxide (NO), measured by chemiluminescence. Exhaled ethane was collected during a flow and pressure-controlled exhalation into a reservoir, discarding dead space air contaminated with ambient air. A sample of the collected expired air was analyzed by chromatography. Compared with normal subjects (n = 14; eight men; age, 33 +/- 2.8 yr), patients with COPD not on steroid treatment (n = 12; FEV(1), 58 +/- 6%) had elevated levels of exhaled ethane (2.77 +/- 0.25 and 0.88 +/- 0.09 ppb, respectively, p < 0.05), CO (5.96 +/- 0.50 and 2.8 +/- 0.25 ppm, p < 0.05) and NO (11.86 +/- 0.53 and 6.77 +/- 0.50 ppb, p < 0.05) levels. Ethane was correlated to FEV(1) (r = -0.67, p < 0.05). Patients receiving steroid treatment (n = 10; FEV(1), 56 +/- 2%) had lower levels of ethane (0.48 +/- 0.05 ppb) than did steroid-treated patients, whereas CO (5.99 +/- 0.63 ppm) and NO (9.11 +/- 0.53 ppb) levels were similar in the two treatment groups. Exhaled ethane is elevated, correlates with FEV(1), and is significantly lower in patients treated with steroids, so it may be complementary to the use of NO and CO in assessing and monitoring oxidative stress in COPD.