AIMS--The corneal epithelial permeability during extended wear of disposable contact lenses was compared with that during daily wear of soft contact lenses. The study was performed to verify whether the extended wear of disposable contact lenses would result in a higher permeability value than the daily wear of soft contact lenses. A higher permeability makes the cornea more vulnerable for bacterial infections and thus could explain the higher incidence of bacterial keratitis found in extended wear of disposable contact lenses in comparison with the daily wear of soft contact lenses. METHOD--The corneal epithelial permeability was determined by fluorophotometry in 33 healthy volunteers after the wear of soft, daily wear contact lenses for at least 6 months. Thereafter the determination was repeated in each volunteer after extended wear of disposable contact lenses for 1 month. The permeability in 34 healthy non-contact lens wearing volunteers was determined as a control. The permeability value was calculated from the amount of fluorescein that passed into the cornea after application by means of an eyebath. RESULTS--The mean permeability values after daily and extended wear were 0.032 nm/s and 0.031 nm/s, respectively. The values were not significantly different (Wilcoxon paired test p > 0.5). The mean permeability for the non-contact lens wearing controls was 0.042 nm/s. CONCLUSION--The results do not sustain the explanation that a difference in permeability value is the main cause of the increased incidence of keratitis during extended wear of disposable contact lenses in comparison with daily wear.