Introduction A patient who had had an elective jejunotransverse colostomy with complete exclusion of intervening bowel underwent radioactive vitamin B12absorption tests before and after reinsertion of 4 inches of ileum into the gastrointestinal stream. Subsequent studies showed that the site of vitamin B12absorption in this patient is the terminal ileum. Report of a Case A 48-year-old woman with intractable obesity (410 lb.) but in otherwise reasonably good health underwent construction of a jejunotransverse colostomy for weight reduction and control (Fig. 1,A). The procedure left 18 inches of jejunum in normal continuity, the remainder of the small bowel and the right half of the colon being excluded. One year after surgery a Schilling test indicated no absorption of vitamin B12. Fourteen months postoperatively, after a steady weight loss amounting to 200 pounds, the bypass was revised by construction of a jejunoileostomy, thus introducing the absorptive