Articular complications are now frequently recognized with jejunoileal-bypass surgery for morbid obesity. We have evaluated 6 referred patients with these problems and 50 consecutive patients who had this procedure. The arthritis is variable but usually affects multiple joints. Four patients were seen during acute attacks of arthritis and all had cryoprecipitable material in their sera and plasma. Three of these 4 patients had evidence of Group D streptococcal antigen present while their joint disease was active, suggesting a possible role for bacterial antigens in the pathogenesis of the arthritis of jejunoileal bypass.