oxidant stress in Chronic Obstructive Pulmonary Disease, asthma, bronchiectasis, cystic fibrosis patients. Quantification of lung oxidative stress in stable COPD patients by measuring ECO levels may also contribute to the understanding of the pathophysiology of COPD. Aims & Objective: To study the utility of measuring Exhaled Carbon Monoxide (ECO) level in addition to Pulmonary Function Test (Spirometry) in the monitoring of Chronic Obstructive Pulmonary Disease (COPD). Materials and Methods: COPD patients who were smokers and with a history of exposure to wood smoke (n =60) and healthy non-smokers as control (n =40) were selected as subjects by fulfilling the exclusion criteria as per the GOLD guidelines. Clinical examinations and spirometry including reversibility test were made following the standard protocol/procedure. ECO was measured using a MICRO III Smokerlyser. Results: The difference in level of ECO between COPD cases and healthy non-smokers was highly significant (F = 23.897; df = 98; p < 0.0001). The difference in the level of ECO among different groups (mild, moderate, severe and very severe) was highly significant (F=15.995; df =2; p