Nine patients were studied 1.5--3 years after jejuno-ileostomy for obesity by an intravenous glucose infusion technique designed to imitate blood glucose concentrations after glucose ingestion. Whereas serum insulin and gastrin concentrations were normal, blood glucose concentrations were significantly depressed compared to preoperative levels as well as to levels in matched normal subjects. Thus, in the fasting state mean concentrations (+/- S.E.M.) of blood glucose, serum insulin and gastrin in the patients were, respectively, 3.3 +/- 0.2 mmol/l, 95 +/- 22 pmol/l and 38 +/- 4 pmol/l. The corresponding concentrations in the matched normals were 4.3 +/- 0.2 mmol/l, 70 +/- 18 pmol/l and 39 +/- 6 pmol/l. The glucose concentrations in the patients were low in all situations, i.e. in the fasting state, after oral glucose ingestion and during the intravenous glucose infusion. The results indicate that jejuno-ileostomy in obesity greatly facilitates peripheral glucose disposal. The mechanism behind this phenomenon is not yet known.