To investigate the alteration of airway mucin in airway disease patients, immunoassay procedures were employed using monoclonal antibodies HM02 and HM03 (Hybridoma, 18,457-463, 1999). Alteration of mucin release was determined by ELISA and the integrity of mucin was determined by Western blot. In ELISA, it was found that mucin release increased from pneumonia, chronic cough, bronchiectasis, eosinophilic pneumonia, lung cancer and bronchial asthma patients. In Western blot, the increase in immunoreactivity was observed in case of pneumonia, chronic cough, bronchiectasis and bronchial asthma. In bronchial asthma, there was no obvious degradation of mucin while in other diseases, varying degree of mucin degradation was observed. The data from the present study implicate that HMO2 and HM03 are suitable for the immunological analysis of mucin in airway disease patients. The role of increased mucin release and varying degree of mucin degradation on airway diseases should be further investigated in the future.