A case of corneal perforation in a patient found to have Mooren's ulcer is presented. The patient was followed up for 1 year both before and after perforation. No evidence of accompanying systemic disease was found. The ulcer healed after excision of the limbal conjunctiva. The subepithelial layer of the conjunctiva was packed with plasma cells. Both IgG and IgM were found in the epithelium as well as along the small vessels. The T-lymphocyte subpopulation was examined three times during the course of the disease; an inverse ratio was always found between the helper and suppressor/cytotoxic T cells.