In order to evaluate two new immunosuppressive agents, FR900506 (FK 506) and 15-Deoxyspergualine (15-DSG), the kinetics of infiltrating cells in the eyes of Lewis rats with experimental autoimmune uveoretinitis (EAU) were studied. Rats were immunized with retinal S-antigen and treated with different doses of either FK 506 or 15-DSG. The inflammatory ocular tissues obtained at various intervals during the process of EAU were examined using an immunoperoxidase technique. The results were compared with those eyes developing EAU without treatment or with suboptimal doses or a suboptimal dose of Cyclosporin (CsA). BothFK 506 and 15-DSG, like CsA, delayed the cellular kinetics during the course of EAU. However. FK 506 had the greatest effect on the kinetics of T lymphocyte subsets by causing the greatest increase in the recruitment time of the T suppressor/cytotoxic population. FK506 treatment resulted not only in the highest inhibition of expression of IL-2 receptors on T cells, but also in the prevention of the expression of MHC class II antigens on ocular resident cells. Treatment with 15-DSG resulted in general immunosuppression on various infiltrating inflammatory cells.