Twelve patients with seasonal allergic conjunctivitis caused by either birch or timothy grass pollen were challenged out of season in both eyes, with the relevant allergen. Itching, redness, swelling, and tearing were assessed on a 0-3 scale. When a positive reaction, i.e., at least 4 points, had occurred in both eyes, one drop of 2% sodium cromoglycate was administered to one eye and one drop of placebo to the other eye in each patient, in a double-blind, randomized fashion. Symptoms were then assessed after 2, 10, 30, and 60 min. Sodium cromoglycate was statistically better than placebo in reducing the symptoms at 2, 10, and 30 min after the treatment had been administered, showing that topical application of 2% sodium cromoglycate can quickly relieve ongoing symptoms of allergic inflammation in the eye.