The purpose of this study was to assess whether a prior bout of exercise enhances passive gut glucose absorption. 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 exercise (n = 8) or rest (n = 7) followed by basal (-30 to 0 min) and a primed (150 mg/kg) intraduodenal glucose infusion [8.0 mg x kg-1x min-1, time (t) = 0-90 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 and 80 min. Phloridzin, an inhibitor of the active sodium glucose cotransporter-1 (SGLT-1), was infused (0.1 mg x kg-1 x min-1) into the duodenum from t = 60-90 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 after each tracer bolus injection. Net gut glucose output in exercised dogs increased compared with that in the sedentary group (5.34 +/- 0.47 and 4.02 +/- 0.53 mg x kg-1x min-1). Passive gut glucose absorption increased approximately 100% after exercise (0.93 +/- 0.06 and 0.45 +/- 0.07 mg x kg-1 x min-1). Transport-mediated glucose absorption increased by approximately 20%, but the change was not significant. The infusion of phloridzin eliminated the appearance of both glucose tracers in sedentary and exercised dogs, suggesting that passive transport required SGLT-1-mediated glucose uptake. This study shows 1). that prior exercise enhances passive absorption of intraduodenal glucose into the portal vein and 2). that basal and the added passive gut glucose absorption after exercise is dependent on initial transport of glucose via SGLT-1.