INTRODUCTION: Urinary recovery of enterally administered probes is used as a clinical test of intestinal mucosal permeability. Recently, evidence has been provided that the recovery of some but not all sugar probes is dependent on the amount of diuresis and renal function. The aim of this study was to assess the effect of fluid loading on the urinary recovery of sugar probes in healthy volunteers. METHODS: In a cross-over study, 10 healthy volunteers ingested 100 ml of a solution containing 0.2 g of 3-O-methyl-D-glucose (3-OMG), 0.5 g of D-xylose, 1.0 g of L-rhamnose, and 5.0 g of lactulose on two different days. The volunteers were randomized to receive either 2 litres of Ringer acetate or no fluid during the following 3 hours. The sugar concentrations were measured in 5-hour urine samples period. RESULTS: Fluid loading increased urine production and urinary recovery of xylose. Fluid loading did not influence the urinary recovery of 3-OMG, L-rhamnose, or lactulose. Neither the lactulose/rhamnose ratio nor the 3-OMG/rhamnose ratio changed. CONCLUSION: Fluid loading increases mediated carbohydrate transport but not the lactulose/rhamnose ratio, after oral sugar administration in healthy volunteers. It remains to be determined whether sugar probes are handled differently in response to fluids in patients with organ dysfunctions.