Data from two short-term double-masked studies using 24 and 16 subjects suggest that topically applied levobunolol safely and effectively treats open-angle glaucoma and ocular hypertension. The onset of effect of a single drop of 0.5% levobunolol occurred within the first hour, producing a maximal hypotensive effect of more than 8 mm Hg after two hours. An intraocular pressure deceased of greater than or equal to 2 mm Hg was still observed after 24 hours for both concentrations of levobunolol tested (0.5% and 1%). Intraocular pressure decreases of more than 9 mm Hg persisted during a one-month trial in which patients were treated twice daily, confirming the results obtained in the 24-hour study. Systemic effects of both timolol (0.5%) and levobunolol (0.5% and 1%) included a consensual intraocular pressure-decreasing effect in the untreated eye and clinically significant reductions in heart rate. Diastolic blood pressure was decreased at two and four hours after administration of 0.5% levobunolol.