Levocabastine is a new topical histamine H I antagonist. The antihistaminic and antiallergic effects of levocabastine eye drops have been evaluated in eight conjuctival provocation studies (n =238). Two studies used a histamine challenge; five studies used allergen challenge; one study used both and in one study allergic provocation was with compound 48/80. In all but one study, only one single dose of levocabastine (one or two drops) was given. Six studies were against placebo only; one was against cromoglycate and one study used both placebo and cromoglycate as reference drugs. Single instillation of levocabastine eye drops protected against histamine and allergen-induced ocular symptoms within a period of 10 minutes. Levocabastine eye drops significantly alleviated conjunctival itching, redness, chemosis, eyelid swelling and tearing induced by histamine or allergen challenge (p ~ 0.05). Four hours after administration levocabastine was still active. With levocabastine, but not with cromoglycate, a significant increase was observed in the allergen threshold. Even when compared to cromoglycate given as a pre-treatment four times daily for two weeks before the allergen challenge, a single dose of levocabastine was significantly more effective in inhibiting hyperaemia, eyelid sweling, chemosis and tearing (all p < 0.05). In conclusion, conjunctival provocation studies have established that levocabastine has a rapid and long-lasting effect in protecting against histamine or allergen-induced conjunctival symptoms.