Abstract: Objective To investigate the role of substance P (SP) in chronic obstructive pulmonary disease (COPD) or asthma. Method Plasma and sputum samples were obtained from 26 COPD patients and 20 asthmatic patients as well as 12 healthy subjects for measurement of SP content. Results Patients with COPD had significantly higher levels of SP in the plasma (7.9±2.6 pmol/L) and sputum (53.8±12.5 pmol/L) than the healthy subjects (3.6±1.7 pmol/L and 6.2±2.3 pmol/L, respectively, P<0.01). The asthmatic patients also had significantly higher SP levels (8.3±3.1 pmol/L and 46.9±10.2 pmol/L, respectively) than the healthy subjects, but there was no significant difference between COPD and asthmatic patients (P>0.05). Conclusion SP may be involved in the airway inflammation process in COPD and asthma.