the operating surgeon, and the intraluminal image was that of pale blue mucosa in which a focus of abnormal vessels was actively oozing bright red blood (Figure 18). This area corresponded to the location of the angiographic blush and was felt to be grossly consistent with an arteri­ ovenous malformation. The area was outlined by hemo­ clips externally, and the colonoscope was slowly with­ drawn for a second look. Decompression of the large bowel was carried out by endoscopic suction during with­ drawal. It was noted that the abnormal vascular pattern was not demonstrable without transillumination even when outlined by silver clips (Figure 1C). Intra-operative colonscopy was completed within 20 minutes. Conserva­ tive wedge resection was performed. The patient's post­ operative course was uneventful. Grossly the wedge of the cecum measured 1.5 x 2 cm and was normal except for a small central mucosal depres­ sion. Microscopic sections revealed a collection of dilated, thin walled blood vessels in the submucosa with penetra­ tion of the muscularis mucosa by some. One vessel could be seen communicating with the lumen (Figure 10). Elastic stains revealed a variable elastic content in the walls with some vessels virtually devoid of elastic tissue. The final diagnosis was arteriovenous malformation.