1. In order to compare the absorption products of sucrose with those of its constituent monosaccharides in man, constant intrajejunal infusions of sucrose and of fructose and glucose were given to six cirrhotic patients with portal-systemic collateral vessels or surgical porta-caval anastomoses. To investigate further the subsequent metabolic fate of fructose and glucose, two further groups of four patients with normal liver function were given constant intravenous infusions of (1) fructose and glucose and (2) fructose, or (1) fructose and glucose and (2) glucose.
2. Solutions containing 292 m-mole/l sucrose, and 277 m-mole fructose and 277 m-mole glucose/l, were used for the intrajejunal infusions. Solutions containing 555 m-mole fructose and 555 m-mole glucose/l, 555 m-mole/l fructose, or 555 m-mole/l glucose, were used for the intravenous infusions. All of the intrajejunal and intravenous infusions were given at 6·0 ml kg−1 hr−1 for 3 hr.
3. During the intrajejunal infusions, blood concentrations of fructose, glucose, insulin, pyruvate, lactate and triglyceride-glycerol were similar with both sugar solutions. In most they were very slightly higher during the sucrose than the fructose and glucose infusions. These differences can be largely accounted for by the small difference in the quantities of the monosaccharides given during the two infusions.
4. The blood concentrations of fructose, glucose, insulin, pyruvate and lactate during the intravenous infusions did not seem to be influenced by the presence of the other monosaccharide. These findings are entirely consistent with the view that in man the constituent monosaccharides of sucrose are handled by separate metabolic paths.