To determine the expression of matrix metalloproteinases (MMPs) in cornea following excimer laser keratectomy, two sets of experiments were performed. In the first experiment, disciform excimer keratectomy was performed on rat corneas. The central regenerating epithelium was harvested at 3-96 h postwounding. MMP levels were assayed in the regenerated central epithelium and the stroma using zymography and immunoblot assays. In the second set of experiments, deep excimer annular keratectomy was performed on rabbit corneas to induce intrastromal epithelial migration. The effect of beta-mercaptomethyl tripeptide, a synthetic inhibitor of metalloproteinase, on the presence and extent of intrastromal epithelial migration was determined. In experiment I, MMP-2 and MMP-9 were expressed in the epithelium of excimer-ablated rat corneas 6-24 h postwounding, but not in the debridement wounds and untreated controls. Only excimer-treated stroma showed MMP-9 activity. In experiment II, intrastromal epithelial migration was delayed by topical application of beta-mercaptomethyl tripeptide, a synthetic inhibitor of MMPs (p < 0.05). After excimer wounds, MMPs are expressed in corneal epithelium and stroma during wound closure. They may play an important role in wound healing after excimer laser keratectomy.