In a double-masked study, 40 patients with primary open-angle glaucoma were randomly assigned to treatment with betaxolol 0.5% or timolol 0.5% in both eyes twice daily. Visual fields and intraocular pressures were studied. Perimetry was performed with the Octopus G1 program two weeks after a washout period and three, six, 12, and 18 months after initiation of treatment. Both drugs reduced intraocular pressure. The reduction in intraocular pressure in the timolol-treated group was more pronounced than that in the betaxolol-treated group; the difference, however, was not statistically significant. In both treatment groups, the visual fields tended to improve during the first six months of treatment and remained stable or tended to deteriorate thereafter. The treatment effect on the visual field was better in the betaxolol-treated group than it was in the timolol-treated group (P = .041).