PURPOSE: Nitric oxide (NO) is an important mediator of inflammatory tissue damage. The present study addresses the question whether inducible nitric oxide synthase (iNOS), and consequently the ability to upregulate NO, is required to effect the pathogenesis of experimental autoimmune uveoretinitis (EAU) in mice. METHODS: Mice with a homologous disruption of the iNOS gene (iNOS KO) were evaluated for their ability to develop EAU and associated cellular responses after immunization with the interphotoreceptor retinoid-binding protein. EAU was determined by histopathology 21 days after uveitogenic immunization, and antigen-specific cellular responses were assessed by delayed type hypersensitivity and lymphocyte proliferation. RESULTS: iNOS knockout (iNOS KO) mice developed EAU with scores similar to wild-type mice and exhibited good cellular responses to the immunizing antigen. CONCLUSIONS: A functional iNOS gene is not necessary for EAU pathogenesis. Therefore, upregulation of NO is not required to mediate autoimmune tissue damage in the eye.