1. Fourteen healthy subjects were investigated before and for 4 hours after oral intake of 75 g of glucose (n = 8) or tap water (n = 6). Whole-body energy expenditure was measured by an open-circuit ventilated hood system. Blood samples for determination of oxygen, carbon dioxide, glucose and lactate were taken from an artery, a hepatic vein and a femoral vein. Blood flow in the splanchnic region was measured by constant infusion of Indocyanine Green. Leg blood flow was measured by venous occlusion strain-gauge plethysmography. Oxygen uptake and carbon dioxide output in the splanchnic and leg tissues were calculated as the product of blood flow and arteriovenous differences in oxygen or carbon dioxide concentrations. Net exchanges of glucose and lactate across the splanchnic and leg tissues were calculated as the product of blood flow and arteriovenous differences in whole-blood glucose or lactate concentrations. 2. Splanchnic oxygen uptake had a biphasic course with an initial increase from 2.35 +/- 0.88 (SD) mmol/min to 2.85 +/- 1.20 mmol/min 30 min after the glucose intake (P < 0.005) and a later decrease below the basal value to around 2.02 mmol/min 90-180 min after the glucose intake (P < 0.05). The integrated increase in the splanchnic oxygen uptake during the 4 h after the glucose intake was -32.6 +/- 49.7 mmol/240 min. Leg oxygen uptake increased from 4.3 +/- 1.4 mumol min-1 100 g-1 to 7.0 +/- 3.2 mumol min-1 100 g-1 90 min after the glucose intake (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)