The nasal mucosa was changed histopathologically by various stimulation and trauma, and especially pH change in the nasal mucosa affects the ciliary activity and lysozyme activity. The author performed an experimental study with the repeated instillation of 2 weeks to 4 weeks, and effects to the nasal mucosa were correlated with histopathological findings. Animals were divided in 4 groups by various solution (phosphated buffer solution(pH 7, 6), citrate buffer solution (pH 5), and acetate buffer solution (pH 4), each being again examined in relation to experimental duration of 2 weeks and 4 weeks. The following results were obtained : 1) A most reliable and advanced pathologic changes were found in pH 4 solution and 4 weeks group. 2) Major histopathologic changes encountered in nasal mucosa included marked edema and congestion, increased infiltration of inflammatory cells, damages of ciliated epithelium including ulceration, goblet cell hyperplasia, metaplastic changes of epithelium, disruption of basement membrane, mucous gland change and mucosal atrophy. 3) Edema and congestion of nasal mucosa, and ciliated epithelium such as loss of cilia and desquamation showed a tendency to be increased roughly relation to the experimental period and change of pH. 4) Infiltration of inflammatory cells was prominent at pH 4 solution group and pH 5 solution group. 5) Irreversible and permanent changes were not recognized during a period of 4 weeks but fibroblastic proliferation, mucosa atrophy and metaplastic mucosal alteration may suggest the process leading to atrophic rhinitis in pH 4 solution group.