A randomised, multicentre parallel group study was undertaken to compare the efficacy and safety of 0.05% azelastine eye drops (101 patients) in an open manner with 0.05% levocabastine eye drops (103 patients) and in a double-blind manner with placebo (103 patients) during a 14-day treatment period involving patients with seasonal allergic conjunctivitis. The three main eye symptoms, scored on a four-point scale, were itching, lacrimation and conjunctival redness; the primary efficacy variable was the responder rate on day 3. Responders were patients whose sum score of the three main eye symptoms decreased by at least three points from a baseline score of at least six points. In addition to these main symptoms, five other symptoms were recorded on days 0, 3, 7 and 14, and patients kept daily diaries of the three main eye symptoms and swollen eyelids. The responder rate after 3 days of treatment was 69% in patients treated with azelastine, 59% in patients treated with levocabastine and 51% in the placebo group. Only the difference in responder rates between azelastine and placebo eye drops was statistically significant (p = 0.02). The improvements in other ocular symptoms and entries in the patients' diaries closely reflected the changes reported by the investigators. No serious adverse events occurred throughout the study. Nine patients (three in the azelastine, five in the levocabastine and one in the placebo group) terminated the study prematurely due to poor tolerability. Adverse drug reactions, mainly a mild, transient irritation and a bitter or unpleasant taste, were reported in 37% of patients receiving azelastine eye drops, 31% of patients receiving levocabastine and 9% of placebo patients. Overall tolerability was assessed as very good or good in 86% of azelastine- and levocabastine-treated patients, and in 95% of the patients receiving placebo. The results of this study indicate that azelastine possesses a tolerability profile at least comparable to that of levocabastine eye drops, but additionally appears to have a slightly quicker onset of effect, and confirm the therapeutic potential of azelastine eye drops in the treatment of allergic conjunctivitis.