Absorption of carbohydrate was quantitated in 49 subjects without disease of the small bowel using a new technique for ileal perfusion. A double-lumen tube with an attached balloon was inserted retrograde through the colon and used to quantify arrival in the ileum of D-xylose and a nonabsorbable marker which had been taken orally. In the same way, absorption of sucrose and the effects of an inhibitor of alpha-glucosidase were also studied. Insertion of the assembly through the colon and intubation of the terminal ileum was usually possible within 30 min; we have designated the technique, endoscopic retrograde bowel insertion (ERBI). The test meals were 500 ml of water containing either 25 g D-xylose and 5 g polyethylene glycol (PEG 4000), or 100 g sucrose with 5 g PEG. Sucrose meals also contained 0, 100, or 200 mg of an inhibitor of alpha-glucosidase (BAYg5421). At the end of a 5-hr test period, the ratio of recovery of D-xylose relative to that of PEG indicated that 69% of D-xylose was absorbed. Five-hour urinary excretion of D-xylose was 31% of that ingested, or 45% of the D-xylose which was absorbed. Sucrose was recovered in ileal samples only when administered together with inhibitor. Rates of sucrose absorption with BAYg5421, 100 and 200 mg, were 75% and 65%, respectively. The perfusion technique of ERBI is a rapid and reproduceable approach to the distal small intestine of man which could be of value in the investigation of intestinal absorption.