OBJECTIVE Azelastine is a selective H(1)-receptor antagonist that inhibits histamine release and interferes with activation of several other mediators of allergic inflammation. Together with demonstrated efficacy in seasonal allergic conjunctivitis, azelastine indicated a therapeutic potential for perennial allergic conjunctivitis (PAC). The present study aimed to evaluate azelastine eye drops in patients with PAC compared to placebo. METHODS A multinational trial in 22 centres randomised 139 patients to twice-daily treatment for 6 weeks with masked 0.05% azelastine eye drops, matching masked placebo, or open-label levocabastine. Randomisation required a sum itching and conjunctival redness score of at least 3 (0-6 scale) after 1 week of placebo. The change in sum score was evaluated during treatment. RESULTS Azelastine significantly improved itching and conjunctival redness compared to placebo (p < 0.001) with global tolerability that was not substantially different from placebo. On day 7, the mean symptoms sum score improved with azelastine by 1.9 +/- 1.1 and with levocabastine by 1.5 +/- 1.2 compared to placebo (0.6 +/- 1.1) from baseline values of 3.7-3.8. The sum scores continued to improve up to day 42. Daily patient logs confirmed the clinically assessed scores. Most frequent adverse events following azelastine were bitter taste and application site reaction. CONCLUSIONS Topical azelastine progressively improved itching and conjunctival redness in PAC patients compared to placebo and was at least as effective as levocabastine. Rapid relief is consistent with H(1)-receptor antagonist action, while continued improvement up to 6 weeks may be consistent with mechanisms involving other mediators of allergic inflammation.