The effects of ileo-jejunal transposition (IJT) on gastro-intestinal hormones and intestinal structure have been studied in 9 mongrel dogs. IJT was performed by isoperistaltic interposition of the distal fourth of the small bowel in the jejunum 15 cm distal from the ligament of Treitz. A test meal (carbohydrate- and fat-rich) loading was carried out in 5 dogs before and 4 and 12 weeks after the operation. Plasma concentrations of gastrointestinal hormones (GLI, GI, GIP and gastrin) were measured by radioimmunoassay using the antibodies. The six mongrel dogs were used for the histological studies. Following IJT hyperenteroglucagonemia was observed, especially in postprandial state. An increase of the mucosal thickness in the whole intestine was observed after IJT. This suggested the possibility that enteroglucagon stimulates intestinal mucosal growth as a circulating hormone. Postprandial plasma GIP levels after IJT were significantly lower at the 90, 120 and 150 min after the test meal loading than those of the preoperative state. Plasma gastrin levels were no significant differences before and after surgery. These observations lead us to conclude that enteroglucagon may play an important role in intestinal adaptation mechanisms after IJT.