In animal models for corneal ulceration, the degradation of extracellular matrix components of the stroma does not occur until after the basement membrane underlying the corneal epithelium has disappeared. Using a thermal-burn model, it was demonstrated that epithelial basement membrane is degraded actively by products of corneal cells in a process that does not require the participation of polymorphonuclear leukocytes. A new gelatinolytic metalloproteinase, preliminarily identified as the matrix metalloproteinase, MMP-9, is synthesized and secreted by corneal cells with a timing appropriate for a role in basement membrane degradation. During healing of ulcers, when new matrix is being deposited actively in the burned tissue, a second new gelatinase appears in the cornea, preliminarily identified as a stable activated form of the matrix metalloproteinase, MMP-2. The timing of expression suggests a role for this enzyme in appropriate deposition and remodeling of new matrix in the regenerating corneal tissue.