We investigated the altered immunolocalization of the components of epithelial basement membrane (BM) in rats with alkali burns of the cornea. Type IV collagen, laminin, and fibronectin were immunohistochemically stained in the alkali-burned corneas after various intervals. Linear laminin immunoreactivity, which represented the localization of the BM, was interrupted, probably by epithelial enzymes, under the regenerating epithelium after 24 h. A normal configuration was restored on day 7, when the central corneal BM showed a type IV collagen immunoreactivity that was not detected in BM of normal cornea. The exact cause of the development of type IV collagen immunoreactivity in the healing BM was not determined. Laminin, type IV collagen, and fibronectin, which were not detected in normal stroma, were all detected in the healing corneal stroma with repopulated keratocytes. Moreover, the BM zone under the regenerating epithelium showed fibronectin immunoreactivity on days 5-14. Distribution of these components of BM seemed to be normal 2 months postburn. The alteration of BM components is thought to be an important marker of the healing process in corneas burned with alkali.