Patients with juvenile rheumatoid arthritis (JRA) commonly develop serious eye disease, particularly chronic uveitis. Most chronic uveitis is idiopathic. Mollicute-like organisms (MLO) were recently reported to be a common cause of chronic uveitis. MLO are pathogenic intracellular cell wall deficient bacteria. No culture system exists for MLO. Disease diagnosis is based on detection using a transmission electron microscope. Uveitis producing MLO are detectable within parasitized intraocular leukocytes. They appear as intracytoskeletal 0.005-0.01 micron diameter filaments and undulating pleomorphic 0.01-1.0 micron tubulospherical bodies. This report describes MLO parasitized lesional leukocytes in the inflammatory eye disease of 5 patients with JRA. Our results indicate that MLO caused the uveitis of these patients. The significance of these findings and rifampin treatment of MLO disease are discussed.