Morphological changes were examined in the corneal endothelium of rabbits after administration of several drugs widely used in ophthalmology. After administration of epinephrine and dipivalyl epinephrine eye drops, swelling of corneal endothelial cells developed; however, these changes were reversible. No pathological changes were observed in the corneal endothelial layer following the administration of timolol, betamethasone, and gentamicin eye drops. Morphological changes were observed in the corneal endothelial layer after the subconjunctival injection of timolol, betamethasone, and gentamicin.