We describe a case of a patient with previously diagnosed of ulcerative colitis, who was admitted to the hospital because of rectal bleeding and abdominal pain. A mild active colitis was reported by colonoscopy with biopsy. Rectal bleeding relapsed, and an arteriovenous malformation in the transverse colon compatible with angiodysplasia was located by early vascular scintigraphy with 99m-technetium-labeled red blood cells. This finding was confirmed by selective arteriography. Four months after hemicolectomy, the patient is free of rectal bleedings. Labeled red blood cell scintigraphy may be useful to differential diagnosis of lower digestive hemorrhage.