Twenty-four patients with bilateral chronic open-angle glaucoma received three treatments: (1) artificial tears (control) in both eyes, (2) artificial tears in one eye and one drop of timolol (0.05%) in the other, and (3) artificial tears in one eye and one drop of betaxolol (0.05%) in the other. Twelve patients always received the test medication in the left eye and 12 in the right eye. The patients were examined and questioned about ocular symptoms at the time of drug administration and at 1, 5, 30, and 60 minutes. Irritation was noted in five treated eyes after artificial tears, in three after timolol, and in 11 after betaxolol. The incidence of irritation after initial treatment was significantly lower than expected for timolol than for artificial tears or betaxolol (P less than 0.01).