Optical and immunofluorescent microscopy was used to examine 52 pathological nasal mucosae (41 allergic, 11 non-allergic), and the results were compared to the clinical, biological and allergic findings. It was noted that there were a large variety of histological lesions in each group of patients, their extent being related much more to the duration and severity of the aggression than to their nature. There appears to be a relation between the extent of the anatomical lesions and immunological activity, non-allergic mucosae being low in immunoglobulin levels.