The corneal epithelium of patients with dry-eye syndrome is stressed by both tear film insufficiency and the frequent use of eye drops (artificial tears). In order to quantify corneal epithelial damage, the permeability of corneal epithelium to sodium fluorescein was determined in 40 consecutive patients with dry eyes (BST less than 10 mm), who did not exhibit visible corneal lesions upon slit-lamp examination. The corneal epithelial permeability of dry-eye patients was shown to be 2.8 times greater than that of individuals without ocular disease. Corneal epithelial permeability of patients using artificial tears containing benzalkonium chloride was increased 3.1 times and that of patients using drops preserved with chlorobutanol only 1.7 times.