Corneal epithelial permeability and autofluorescence were measured by fluorophotometry in patients with open-angle glaucoma or ocular hypertension to quantify the epithelial function of the cornea and to evaluate its metabolic activity in 24 patients using daily timolol and 11 not using timolol. The findings were compared with those in age-matched healthy controls. Permeability values in patients using timolol were 1.9 times higher than in patients not using timolol and 2.5 times higher than in healthy controls (Mann-Whitney test P < 0.001). Values for patients not using timolol did not differ from those for healthy controls (P = 0.15). Corneal autofluorescence values in each patient group were higher than in healthy controls (P = 0.002). CONCLUSIONS (1) open-angle glaucoma or ocular hypertension alone does not affect corneal epithelial permeability; (2) daily instillation of timolol causes impairment of the corneal epithelial barrier; (3) open-angle glaucoma or ocular hypertension are likely to induce an increase of corneal autofluorescence.