Levocabastine is a new selective H1 receptor antagonist. The effect of the drug administered locally was compared to placebo in a quantified nasal and conjunctival provocation test with allergens performed in patients allergic to grass pollen. In the nasal provocation test, levocabastine was able to increase the 'reaction threshold' (dose of allergen necessary to trigger allergic symptoms) in 9 out of 12 patients; the drug inhibited rhinorrhea and sneezing, but not nasal obstruction. In the conjunctival provocation test, the 'reaction threshold' clearly increased in 10 out of 11 patients. The local administration of levocabastine might be useful in allergic rhinitis and conjunctivitis.