This double-blind, randomised, placebo-controlled study was carried out to assess the efficacy and safety of 0.025% and 0.05% azelastine eye drops twice daily administered for 14 days to patients with seasonal allergic conjunctivitis or rhinoconjunctivitis. A total of 278 patients were recruited and 226 patients were evaluable for per protocol analysis. The target parameter was the response rate. Four eye symptoms, including the main symptom (itching) were recorded by patients in diaries and eight symptoms were assessed by physicians before and after seven and 14 days of treatment. Severity of symptoms was measured on a four-point scale. The response rates for itching (improvement of at least one score point within the first three days) according to patient assessment were 43% for placebo, 52% for 0.025% and 56% for 0.05% azelastine (NS). However, a more objective assessment of the three main eye symptoms by physicians showed a concentration-dependent improvement in response rate compared with placebo (a decrease of > or = 3 points from a baseline total score of > or = 6), which reached statistical significance for 0.05% azelastine on Day 7 (p < 0.002). In the evaluable patient population, the scores of the three main eye symptoms as well as of all eight recorded eye symptoms, as assessed by the physician, were significantly (p < 0.05) lower in the 0.05% azelastine eye drops group in comparison with the placebo group at Day 7. Inefficacy was the cause of withdrawal in five and three patients on 0.025% and 0.05% azelastine, respectively, and in six patients on placebo. Adverse drug effects, mainly a mild, transient irritation and a bitter or unpleasant taste, were reported by 14% (0.025%), 20% (0.05%) and 15% (placebo) of the patients. No serious side-effects occurred. Azelastine eye drops are effective and well tolerated at a concentration of 0.05% for the treatment of seasonal allergic conjunctivitis.