Eligible COPD patients (newly diagnosed or untreated for at least 3 months) will be enrolled at out-patient clinic after consenting by participants. Upon enrollment, exhaled NO (eNO) will be measured and patients will be categorized into 2 groups according to eNO levels: either high exhaled NO (greater than or equal to 23.5 ppb) or low eNO (\< 23.5 ppb) group. In each group, patients will be randomized to receive either 2 inhalations of fluticasone/salmeterol 250/25 mcg/ pudd twice daily or 2 inhalations of tiotropium 2.5 mcg/inhalation for 12 weeks and followed at scheduled visits. Testing outcome measures include eNO, lung function, different count and mediators in induced sputum, and which will be tested as the following timings: before (baseline, week 0), and after treatment (week 4 and week 12). Rescue medication and drug compliance will be record.
