INTRODUCTION Fractional exhaled nitric oxide (FeNO) has been used as a marker of airway inflammation. Airway caliber is related to the level of FeNO in asthmatics. OBJECTIVES This study aimed to investigate whether airway obstruction could interfere with real FENO levels and if different FeNO changes after albuterol inhalation could assist in distinguishing asthma from chronic obstructive pulmonary disease (COPD). METHODS FeNO and spirometry measurements were performed before and after albuterol inhalation in the following three patient groups: 30 steroid-naive asthmatics, 25 asthmatics inhaling corticosteroids/long-acting β(2)-adrenergic agonists for at least 1 month and 20 COPD patients. Bronchodilator test (BDT) results were positive in all patients enrolled. The correlations among FeNO levels, pulmonary function and sputum eosinophil counts were analyzed. RESULTS FeNO increased significantly after albuterol inhalation in steroid-naive asthmatics but not in ICS-treated asthmatics or COPD patients. The FeNO levels demonstrated no significant correlation with spirometry results or sputum eosinophil counts before or after inhaling bronchodilator in all three groups. Both the levels of FeNO and changes in FENO after albuterol inhalation in steroid-naive asthma patients were higher than those in ICS-treated asthmatics and COPD patients (P < 0.001). The differences remained after proper adjustment for confounding factors (gender, age, smoking pack-years, ICS-treated and pulmonary function index). CONCLUSIONS Our results support the role of FeNO in differentiating asthmatics from COPD patients with positive BDT. FeNO detection after albuterol inhalation should be encouraged in steroid-naive asthma patients with airway obstruction.