The corneal buttons after corneal graft of 22 patients with herpetic keratitis were studied (16 male, 6 female; 7-87 years of age). Ten still had active inflammation, while 12 had stabilized by the time of the study. Different degrees of neovascularization were observed in 19 cases. HLA-DR antigen was detected in the corneal epithelium in 7 of 22 cases (32%), in the corneal stroma in 17 of 22 cases (77%), and in the endothelium in 9 cases (41%) by using the immunohistochemical technique. The expression of HLA-DR antigen was more common and more marked in active herpetic keratitis (90%) and in neovascularized corneas (84%). The frequency and density of HLA-DR expression in perforating corneal ulcers were no higher than in other cases, but anterior synechia was accompanied by strong expression of HLA-DR antigen in the corneas. The expression of HLA-DR antigen was not only detected in the peripheral, but also in the central area of the specimens. The cells expressing HLA-DR antigen in corneas were mainly corneal cells. The results showed a close relationship between HSV-keratitis and the expression of HLA-DR antigen, which may be induced during the clinical course of the disease. The expression of HLA-DR might be one of the factors in the recurrent onset of the disease and a significant sign of the prognosis of corneal transplantation for these patients.