To identify the infiltrating mononuclear cells in conjunctival lesions, we stained frozen tissue sections of conjunctiva with a series of monoclonal antibodies against T cells and T-cell subsets with an immunoperoxidase method. In vernal conjunctivitis and ocular pemphigoid, most lymphocytes reacted with the anti-T4 antibodies that define helper/inducer T cells (T4+); a minority reacted with the anti-T8 antibody that defines suppressor/cytotoxic T cells (T8+). However, T8+ cells predominated in a conjunctival specimen from a patient with chronic graft-vs-host disease. A few T8+ cells and rare T4+ cells were also found in normal conjunctiva. In some diseased conjunctivas, there was an increase in cells stained with anti-T6 antibody, which stains Langerhans cells in normal conjunctiva and skin. T lymphocyte subsets and Langerhans cells probably play an important role in the pathogenesis of inflammatory conjunctival lesions.