To investigate the changes in the corneal epithelial basement membrane following an alkali burn, we examined the immunolocalization oftype IV collagen and laminin in the eye of the guinea pig burned with alkali. The burn damaged the corneal, limbal and conjunctival epithelium. After regeneration, basement membrane was interrupted, as indicated by laminin immunoreactivity. Type IV collagen immunoreactivity was transiently expressed in the early healing phase in the epithelial derived from both the cornea and conjunctiva, but was not seen in the normal corneal epithelial basement membrane. Later in the healing process, following transdifferentiation of the conjunctival epithelium into a cornea-like epithelium, its type IV collagen immunoreactivity was weaker than that in the basement membrane of the nontransdifferentiated epithelium. Conjunctival transdifferentiation during healing may have led to transient development of type IV collagen immunoreactivity.