The non specific nasal hypersensitivity (N.S.N.H.) is characterized by an exaggerated reaction towards various non-specific stimuli in rhinopathic subjects. This N.S.N.H. involves the afferent structure of nasal mucosa, the effector organ and the central modulation system. The physiopathogenetic and clinical implications induced the authors to study the N.S.N.H. behaviour in 218 subjects divided into 5 groups, as follows: control group, subjects with perennial rhinitis of non allergic origin, subjects with seasonal rhinitis due to allergy towards Graminaceae during seasonal crisis and not, subjects with perennial rhinitis due to allergy towards Dermatophagoides pteronissinus. All subjects moreover have been subdivided according to the years of illness. The N.S.N.H. behaviour has been studied with non-specific nasal provocation tests with methacholine, cold water solution and histamine, so the amount of sneezes were assessed. The results show a reduction of the reaction, previously high, to methacholine and cold water solution tests after 6-12 years of illness in subjects with perennial rhinitis, while the test with histamine always gives higher results. This could mean a reduction of N.S.N.H. during the years of illness, probably connected to the answer of the effector organ, without involvement of that afferent portion of nasal mucosa.