The purpose of this study was to assess whether a prior bout of prolonged moderate exercise enhances gut glucose absorption due to an increase in passive absorption. For this purpose, fifteen mongrel dogs had sampling catheters, infusion catheters, and a portal vein flow probe implanted 17 days before an experiment. Protocols consisted of either 150 min of moderate exercise (n=8) or an equivalent period of rest (n-7) followed by basal (-30 to 0 min) and a primed (150 mg^.kg^-1) intraduodenal glucose infusion (8.0 mg^.kg^-1.min^-1, t=0 to 90 min) periods. 3-O-[³H]methylglucose (absorbed actively, facilitatively, and passively) and L-[¹⁴C]glucose (absorbed passively) were injected into the duodenum at t=20 min and 80 min. Phloridzin, an inhibitor of the active SGLT1 glucose transporter, was infused (0.1 mg^.kg^-1.min^-1) into the duodenum from t=60 to 90 min with a peripheral venous isoglycemic clamp. Duodenal, arterial, and portal vein samples were taken every 10 min during the glucose infusion as well as every minute during the 5 min following each tracer bolus injection. Net gut glucose output (NGGO) in the exercised dogs increased compared to the sedentary group (5.34±0.47 and 4.02±0.53 mg^.kg^-1.min^-1; p<0.05). Passive gut glucose absorption increased by ~100% following exercise (0.93±0.06 and 0.45±0.07 mg^.kg^-1.min^-1; p<0.05). Transport-mediated glucose absorption increased by ~20% but the change was not significant. The infusion of phloridzin eliminated the appearance of both glucose tracers in sedentary dogs, suggesting that passive transport required SGLT1 mediated glucose uptake. This study shows that prior exercise 1) enhances passive absorption of intraduodenal glucose into the portal vein and 2) that basal as well as the added passive gut glucose absorption following exercise is dependent on initial transport of glucose via SGLT1.