Corneal tissue obtained during superficial keratectomy from a patient with herpesvirus disciform keratitis was studied by immunoelectron microscopy. Clinically, this cornea had a dense central infiltrate with a circumferential opaque ring histologically resembling the immune ring described by Wessely. Histologically, along the line of altered keratocytes and ground substance, an infiltration of inflammatory cells was found. Herpesvirus particles were seen by electron microscopy in the corneal stroma, but these virus particles had abnormal, noninfective forms such as empty capsids and incomplete virions. By immunoelectron microscopy with a peroxidase-labeled antiherpesvirus antibody reagent, herpes-virus antigens were localized inthe corneal keratocytes and in the corneal stroma. The major localization of the virus antigens was in association with the herpes virions and surrounding vacuoles in the keratocyte nucleus and in the corneal stroma in the area of degenerating keratocytes. These findings support the view of a hypersensitivity mechanism in the pathogenesis of herpes simplex virus disciform keratitis.