Perennial allergic diseases of the upper respiratory tract are becoming more and more frequent. Treatment is difficult and indicated only if there is clear evidence that the suspected allergen definitely causes the symptoms. To date the intranasal allergen provocation test (INT) is the only possibility to prove the actuality of an allergen at the shock organ (e.g. the nasal mucosa). However, the validity of the INT is diminished because the test is handled differently by various authors. In this study we therefore examined the extraseasonal reproducibility of INT in 21 patients allergic to graminaceae. After determination of an individual allergen concentration for every subject the INT was repeated five times under standardised conditions (allergen lyophilised and standardised in biological units, application of the allergen solution to the inferior concha, rhinomanometrical measurement of the nasal flow before and 15 min. after the provocation). Using a flow reduction of 30 per cent as borderline value we found a high reproducibility of the INT. The nasal reaction was not diminished after repeating the test within 24 hours. The essential and so far unsolved problem of the INT is not due to the technical device but to the concentration of the allergen solution which must correspond to the natural exposition of the patient.