We examined human corneoscleral tissue for cells that are phenotypically similar to known antigen-presenting cell (APC) populations. Antigen-presenting cells are involved in the uptake and processing of antigen for presentation to T lymphocytes, thereby playing a central role in induction of the immune response. The recognition of antigen by T lymphocytes requires that an APC express major histocompatibility complex class II molecules. Using immunoperoxidase staining techniques, the presence of cells expressing class II glycoproteins and T-cell subsets were determined. The staining patterns of the trabecular meshwork, ciliary body, cornea/sclera, and conjunctive are described for monoclonal antibodies OKT6, OKM1, HLA-DR, and HLA-DQ, and T-cell markers OKT8, Leu-3a, and Leu-4. The results of the present study demonstrate that the anterior chamber contains a network of immunocompetent cells. The presence of a subpopulation of cells within the anterior chamber that express class II glycoproteins of the major histocompatibility complex suggests this tissue may play an important role in immune regulation within the eye.