Purified S-antigen was used to induce experimental autoimmune uveitis in 42 guinea pigs. 16 animals were used as controls. Footpad immunization with fresh bovine S-antigen in physiologic saline mixed with complete Freunds's adjuvant induced a clinical disease in 95% of the eyes in test animals.In aqueous humour the increase in phospholipase-A2and proteins as well as myeloperoxidase measured from iris-ciliary blocks correlated well with the severity of uveitis evaluated by clinical grading. Leukotriene C. and prostaglandin E2were only elevated in aqueous humour arawn from eyes showing a mild form of uveitis. Neither leukotriene C4nor prostaglandin E2were detected in eyes graded as clinically moderate or severe.In serum samples phospholipase A2leukotriene C4prostaglandin E2and gamma glutamyf transpeptidase were measured. Of these biochemical parameters, only gamma glutamyl transpeptidase was significantly elevated in test animals with experimental autoimmune uveitis.Histological analysis revealed focal mononuclear cell infiltrations in the choroid. Mononuclear as well as polymorphonuclear cell infiltration was seen predominantly in the pars plana region of the ciliary body of test animals with uveitis. Simultaneous destruction of the outer segments of the photoreceptor layer was seen.