In a double-blind study, 30 patients with ocular hypertension were randomly assigned to receive one drop of 0.5% befunolol or placebo (the drug vehicle) in each eye twice daily for 120 days. The befunolol used contained no preservatives. Before and after treatment the number and shape of the endothelial cells of the five corneal sectors were evaluated. After 120 days of twice-daily application of befunolol or placebo, no changes in the shape or density of the corneal cells were found in any patient. No differences in the patients receiving befunolol or placebo were noted. The consensual ophthalmotonic reaction was studied in 15 of the patients before and after befunolol administration. A significant decrease in intraocular pressure was noted at 30 minutes and at 1, 2, 3, 4, 5, and 6 hours after befunolol. Intraocular pressure also decreased significantly at 1 to 4 hours after placebo, and then returned to pretreatment levels at 6 hours.