The new H1-receptor antagonist levocabastine is the most potent antihislumine available, as shown in classical animal tests for antihistamine activity. Its effects also are very specific, with doses as high as 40000 times the effective antihistumine dose not displaying other pharmacological effects. In nasal and ocular provocation tests, levocabastine nasal spray and eye drops protected against allergen-induced nasal and ocular symptoms. Twenty-three clinical trials have been performed with levocabasline nasal spray in 1363 patients with allergic rhinitis. At a dose of two sprays per nostril twice daily (if necessary to be increased up to four times daily), levocabastine was significantly better than placebo and as good as or slightly better than cromoglycate in alleviating nasat symptoms. Good to excellent results were reported in about 60% of patients on levocabastine. compared with 37% with placebo and 47% with cromogly-cate. Levocabastine eye drops were studied in 21 clinical trials including 1218 patients with allergic conjunctivitis. One drop per eye twice daily (up to four times daily) provided significantly better symptom control than placebo and similar effects as those observed with cromoglycate. Response rates were 71-80% with levocabastine, 55% with placebo and 76% with cromoglycatce. Levocabastine has a fast onset of action, with 94% of patients experiencing symptom relief within 15 min after the first instillation of levocabastine eye drops. Three long-term studies (10-16 weeks' duration) showed absence of tachyphylaxis during prolonged treatment with levocabastine. The incidence of adverse experiences was similar for levocabastine, cromoglycate and placebo, for nasal spray as well as eye drops. Nasal and ocular irritation were the most frequently reported complaints. No consistent changes in haematological or biochemical variables were observed. Levocabastine promises to be a valuable topical alternative for the treatmenl of patients with allergic rhinoconjunctivitis.