In order to learn about the immunopathogenic mechanisms of experimental autoimmune uveoretinitis (EAU), the capacity of lymphocytes to transfer the disease was studied. EAU was transferred to naive syngeneic rats by intraperitoneal injection of spleen or lymph node (LN) cells from S-antigen immunized rats, following their incubation in culture with either S-antigen or concanavalin A (Con A). In contrast, the same cells did not cause inflammatory changes in the recipient eyes when injected intravitreally. The identity of the lymphocytes that transfer EAU was determined by using monoclonal antibody enriched subsets of lymphocytes. EAU was transferred by the subset of helper/inducer T-cells, but not by T-cells of the suppressor/cytotoxic subset. Recipient rats of spleen or LN cells cultured with S-antigen exhibited both humoral and cellular immune responses to S-antigen. On the other hand, recipients of spleen cells cultured with Con A developed only cellular immune response to S-antigen. Yet, both groups of recipients fully developed EAU. The clinical and histologic changes in recipient rats closely resembled those in rats in which EAU was induced by active immunization. Severe tissue damage occurred at the photoreceptor cell layer, but inflammatory infiltration also was found in other ocular tissues. Involvement of polymorphonuclear leukocytes (PMNs) was noted throughout ocular tissues even in the eyes of recipients with no detectable antibodies to S-antigen, suggesting that the ocular PMNs infiltration in rats is not necessarily the result of an Arthus-like inflammatory process.