Nine patients with progressive bilateral Mooren's ulcer unresponsive to conventional ocular and systemic therapy were treated with methotrexate or with cyclophosphamide. The progressively destructive inflammatory process was arrested, and ocular anatomy and function were preserved, in eight patients who were adequately treated with immunosuppressive doses of the cytotoxic drugs for 6 to 24 months. The inflammatory process eventually destroyed both eyes of one patient who received inadequate therapy and follow-up care. Used properly, cytotoxic immunosuppressive therapy may offer a reasonable option in the care of patients with bilateral progressive Mooren's ulcer.