The nasal mucosa will be changed histopathologically by various factors. Particularly, the pH change in nasal discharge, which affects the ciliary activity and lysozyme activity, is important. The pH of nasal cavity will be changed due to acute and chronic inflammation from neutral to acid or alkali side. The authors measured the pH of nasal cavity from 100 patients, who had chronic paranasal sinusitis, of the patients who visited the Department of Otolaryngology, Seoul Red Cross Hospital during from August 1984 to July 1985 and from 30 normal persons who had not nasal symptoms and history of antibiotic therapy recently. The following results were obtained. 1) The average pH of nasal discharge in normal was 7.12 and the range of pH was from 6.6 to 7.8. 2) The average pH of nasal discharae in chronic paranasal sinusitis was 7.01 and the range of pH was from 6.4 to 7.6. 3) The pH of nasal discharge in normal was rather neutral than acid, and the pH of nasal discharge in chronic paranasal sinusitis was more acid than the pH of nasal discharge in normal.