The essential ways in the nose serve the body as the site of olfaction, an airway to the lower respiratory tract, and organ for the preparation of the inspired air for the pulmonary surfaces and a selfcleansing structure. The nasal mucosa was changed histopathologically by various external stimulation and trauma, and especially pH change in nasal discharge effects the ciliary activity and lysozyme activity. The author performed an experimental study with the repeated instillation of alkaline solution into the nasal cavites of 36 white rats during period of 2 weeks to 4 weeks, and effects to the nasal mucosa were correlated with histopathologic findings. The following results were obtained. 1) A most reliable and advanced pathologic changes were found in more alkaline groups and 4 weeks group. 2) Major histopathologic changes encountered in the nasal mucosa were edema and congestion, squamous metaplasia and goblet cell hyperplasia. 3) Alkaline solution couldn't do a mechanical change to the cilia and the ciliated epithelium, and couldn't develop remarkable purulent inflammatory change in the nasal mucosa. 4) Irreversible and permanent chages were not noted during a period of 4 experimental weeks, but one of mild mucosal atrophy in group 5 was recognized.