This paper describes the spontaneous occurrence of an autoimmune uveoretinitis in nude (nu/nu) mice reconstituted when 4 weeks old by the grafting of rat embryonic thymus. The uveoretinitis was characterized histologically by progressive loss of the pholoreceptor layer, observed in 4.0, 17.6, 42.9% and 71.4 % of such mice at 3, 5, 7 and 12 months of age. respectively. Mice with uveoretinitis were shown to huve serum IgG antibody reactive by indirect immunofluorescence with retinal photo receptors, and with interphotoreceptor retinoid-binding protein (IRBP). but not retinal S-antigen. by immunoblotting and ELISA. A uveoretinitis could be adoptively transferred to syngeneic ungrafted nude mice by splenic CD4* T cells from diseased animals. This is the first experimental model of a (T cell mediated) autoimmune uveoretinitis which develops spontaneously and which is not dependent upon deliberate sensitization with retinal antigens and adjuvants.