Triptase is an enzymatic protein found in the mastocytes. Although the biological role of this substance is not fully understood, significant amounts of it are found in the nasal secretions of allergic subject both when naturally exposed to the allergen and when subject to specific nasal provocation tests. The present study uses a radioimmunological method (Pharmacia, Uppsala, Sweden) to assay the amount of triptase in two groups: one composed of 10 subjects suffering from allergic rhinitis and the other of 10 non allergic controls. All subjects were submitted to nasal wash with a saline solution prior to endonasal administration of an allergen extract (Poa Pratensis or Dermatophagoides Farinae). Fifteen minutes after nasal provocation the nose was once more washed out with a saline solution. All the wash liquids, both before and after stimulation, were assayed to determine the triptase content and the results for the two groups were compared. The results did not follow a normal distribution and were compared. The results did not follow a normal distribution and were processed with non parametric statistical methods. The allergic subjects showed base values, of 1.4 U/l (mean) while after allergic stimulation this jumped to 14.5 U/l (mean) (p < 0.005). On the other hand, the pre- and post-stimulation values were comparable for the non allergic group. In addition, there was no statistically significant difference between the basic pre-trial triptase levels in the allergic and non allergic subjects. The results indicate that assaying the triptase content in nasal wash liquid can provide a useful support in the diagnosis of allergic rhinitis.