BACKGROUND: Chronic cough is a common non-specific symptom and has various causes including asthma. OBJECTIVE: The aims of this study were to compare eosinophilic degranulation in the airways between chronic cough patients with and without asthma and to evaluate correlations between sputum eosinophils and eosinophilic degranulation proteins. METHOD: Thirty-seven patients with chronic cough and 9 normal individuals (control group) were enrolled. Patients with chronic cough were divided into 2 groups based on positivity for bronchial hyperresponsiveness (BHR): those with asthma (asthma group, n=18) and those without asthma (non-asthma group, n=19). Sputum levels of eosinophil-derived neurotoxin (EDN) and major basic protein (MBP) levels were measured, and eosinophil counts were performed in all patients. RESULT: Sputum % eosinophils were increased in both the asthma and non-asthma groups compared to the control group. However, sputum EDN/MBP levels were increased only in the asthma group compared to the non-asthma and control groups. Sputum % eosinophils correlated positively with sputum EDN/MBP levels in the asthma group, but not in the Non-asthma group. CONCLUSION: Increased EDN/MBP levels and significant correlations between % eosinophils and EDN/MBP levels were observed only in the asthma group, suggesting that eosinophil degranulation proteins could be a marker for identifying chronic cough due to asthma.