Autoimmunity directed against retinal or choroidal antigens has been suggested to play a role in the chorioretinal lesions observed in patients with Fuchs' heterochromic cyclitis. This hypothesis was addressed and patients with Fuchs' heterochromic cyclitis were tested for cellular immunity (migration inhibitory factor assay) against human retinal S-antigen. A significantly higher percentage of patients with Fuchs' heterochromic cyclitis had a positive cellular autoimmune response to S-antigen than healthy controls and other patients with anterior uveitis. This finding is remarkable since Fuchs' heterochromic cyclitis is generally classified as an anterior uveitis and patients with Fuchs' heterochromic cyclitis without chorioretinal lesions also had a positive test. In view of these results and a sensitisation against a corneal antigen reported earlier in Fuchs' heterochromic cyclitis, it is suggested that a chronic low grade grade anterior uveitis or chorioretinitis of unknown origin may cause the release of potent autoantigens in these patients.