The efficacy and tolerability of azelastine (CAS 58581-89-8) eye drops at three different doses (0.025%, 0.05% and 0.1%) were investigated in a double-blind, randomized, placebo-controlled, crossover study in 24 subjects with a history of allergic conjunctivitis/rhinoconjunctivitis, who were challenged, out of season, by airbone allergen in the "Vienna Challenge Chamber" (VCC). Subjects received a single dose of azelastine eye drops 60 min before the start of a 4 h challenge in the VCC. Additional local challenge, mimicking a gust of wind, was administered 15 min before the end of the session. Each of the 4 study days was separated by a 2 week washout period. Azelastine eye drops showed a dose-dependent inhibition of the development of itching of the eyes. The effect was most pronounced 15 min after the additional local challenge. A maximal effect was achieved at a dose of 0.05%. Similar effects were observed on lacrimation. Azelastine eye drops also dose-dependently inhibited the degree of conjunctival redness, measured by digital imaging, and tended to reduce the low incidence of chemosis observed. Ranking of the results of all symptoms for each treatment group confirmed the optimal effect at a dose of 0.05%. Azelastine eye drops had no effect on nasal and bronchial symptoms or on measurements of airways function (FEV1). No adverse effects of the treatments were reported. The data support the use of 0.05% azelastine eye drops in the treatment of allergic conjunctivitis/rhinoconjunctivitis.