Chemical burns were produced using a 4 N NaOH solution in 21 rabbit corneas. The ultrastructural findings were examined under an electron microscope five minutes and 1, 2, 4, 8, 15, and 30 days after the burn. A morphologic disturbance of the basement membrane and its complexes was detected from the first day of the experiment. These findings suggest that the basement membrane plays an important role in the pathogenesis of corneal recurrent erosions and ulcer formation after chemical burns.