Frozen sections of normal Balb/c corneas and corneas from Balb/c mice with Klebsiella keratoconjunctivitis were examined for the expression of class I, class II H-2 antigens and MAC-1 antigens using monoclonal antibodies in an immunoperoxidase technique. Class I antigens were readily detected, in both normal and diseased corneas, mainly in the epithelium. Class II (Ia) and MAC-1 antigens were not detected in the normal corneas. However, these two antigens were found mainly in the epithelium and to a lesser extent in the stroma of corneas from keratoconjunctivitis mice. Both normal and diseased corneas were furthermore shown to be peroxidase-. Since Langerhans cells (LC) are Ia+, MAC-1+, and peroxidase- cells, we conclude that although the normal mouse cornea is devoid of these cells, under bacterial infection LC infiltrate the corneal epithelium.