24 different antigenic preparations from bovine or guinea pig retina and 3 from bovine uvea were tested for their ability to induce uveo-retinitis in guinea pigs. Each animal received one injection into the hind foot pads of 0.1 ml og the tissue preparation mixed with an equal volume of complete Freund's adjuvant. The intensity of the disease was assessed by clinical and histological criteria. Homogenates and extracts from whole guinea pig retina are more active than the same preparations from bovine retina. Autologous retinal extract is slightly more active than homologous in low doses. In bovine retina, the autoantigen(s) is localized in the photoreceptor structures and the pigment epithelium. Bovine uveal preparations seem to be inactive when the epithelium has been removed. Purified outer segments are very active, as well as soluble extracts of outer segments. Highly purified bovine rhodopsin has no immunopathogenic activity. A soluble autoantigen (autoantigen S) has been isolated by preparative isoelectrofocusing from retinas of several species. Autoantigen S from guinea pig induces the disease in guinea pigs at a dose of a few micrograms.