Pineal glands of rats with experimentally induced autoimmune uveitis (EAU) were studied histologically. Inflammatory changes, characterized by mononuclear infiltration, were found in the pineal glands of one-third of the Lewis rats that developed EAU by active immunization with S-antigen. No changes in the pineal gland were observed in AVN rats which are "low responders" for EAU and did not develop ocular disease. Frequency and severity of both pineal gland and ocular involvement clearly were elevated by intravenous injection of Bordetella pertussis along with the S-antigen immunization; all B. pertussis-treated rats of both Lewis and AVN strains developed pineal and ocular changes. Inflammatory changes of the pineal gland also were found in rats in which EAU was induced passively by transfer of lymphocytes from S-antigen-immunized donors. The frequency of involvement of the pineal gland was found to be lower than that of the retinas in rats where EAU was induced by active immunization or by adoptive transfer of lymphocytes.