Iris and ciliary body of mouse eyes have been examined for the presence of bone marrow-derived cells possessing the capability of functioning as antigen-presenting cells (APC). We have determined that iris and ciliary body contain significant numbers of cells bearing T200, indicating their bone marrow origin. Most of these express the F4/80 marker typically found on mature macrophages. However, approximately one-third of the cells express Ia and a similar number express Mac-1 markers. Virtually none of the cells express Thy-1 or surface immunoglobulin. Whole preparations of excised iris/ciliary body, or single cell suspensions prepared from these tissues were then assayed for their capacity to induce proliferation among allogeneic lymphocytes. It was discovered that iris/ciliary body tissues or cells did not function as alloantigen-presenting cells, although tissue and cells derived from the corneal limbus were allostimulatory. In addition, iris/ciliary body tissues and cells displayed the ability to suppress mixed lymphocyte reactions to which they had been added as regulatory cells. We conclude that normal iris and ciliary body contain bone marrow-derived cells that fail to function as alloantigen-presenting cells. However, cells were present that have the capacity to inhibit alloimmune lymphocyte proliferation. The strategic location of inhibitory cells in the tissues that line the anterior chamber of the eye raises the possibility that these cells may play a role in the phenomenon of immunological privilege that is characteristic of this site.