Episodes of catastrophic entero-colitis associated with mesenteric vascular insufficiency in patients with rheumatoid arthritis(RA) have rarely been recorded thus far. We herein report two cases of RA complicated with severe attacks of entero-colitis presumably due to mesenteric vasculitis. Surgical intervention was necessary in the first case, while the second patient recovered well only through conservative therapy. Case 1: A 74-year-old man with history of RA since 1985 started to complain of abdominal discomfort and nausea early in February, 1989. On February 12, Episodes of tarry stool developed. Rapid down-hill clinical course prompted laparotomy under the clinical diagnosis of peritonitis. Ischemic changes were observed at the ileum end, the entire length of which was 120 cm orally from the cecum. The site was resected. Multiple linear and aphthoid ulcer lesions were discovered throughout the entire lumen. Histopathologically, evidence of necrotizing vasculitis such as fibrinoid necrosis and mural thrombi was demonstrated in small arteries of the submucosal layer underlying the ulcer lesion. Case 2: A 63-year-old woman who had been suffering from RA since 1980 noticed the onset of nausea, abdominal pain and bloody diarrhea in July, 1989. Colonoscopy examination revealed multiple linear and aphthoid ulcers in the sigmoid colon which was presumed to be due to ischemia. Laboratory evaluation at that time demonstrated hypocomplementemia, positive circulating immune complex and high titer of anti-DNA antibody. Corticosteroid therapy with moderate dose was successful in alleviation of all the abnormal findings and the patient fully recovered three months after her initial GI episode.