We prospectively studied 12 patients to compare fibreoptic enteroscopy and methylene blue injection through superselectively prepositioned angiographic catheters in intra-operative localization of bleeding small intestinal lesions. Four patients were excluded because the lesions were easily detected by gross examination. Eight patients were subjected to study by these two methods. As methylene blue injection required a positive angiography, it was possible only in five patients. In two of these five patients, non-bleeding lesions were present outside the intestinal segments localized by this method. Enteroscopy was simple, accurate and reliable in seven patients. Complete enteroscopy was impossible in one patient with advanced lymphoma because the intestine and its mesentery were matted together. Fortunately, the bleeding ulcers were still within the reach of the endoscope. Enteroscopy localized bleeding small intestinal lesions more exactly than methylene blue injection so that the length of gut resection could be shorter. We, therefore, conclude that enteroscopy is the better intra-operative localization procedure.