Improved glucose tolerance to sequential glucose loading (Staub-Traugott effect) is an important determinant of day-to-day glycemic exposure. Its mechanisms have not been clearly established. We recruited 17 healthy volunteers to receive two sequential OGTTs, at time 0-min and 180-min (Study I). The protocol was repeated on a separate day (Study II) except that plasma glucose was clamped at 8.3 mmol/l between 60-180min. -cell function was analyzed by mathematical modeling of C-peptide concentrations. In a subgroup, glucose kinetics were measured by a triple-tracer technique (infusion of [6,6-²H₂]-glucose and labeling of the 2 glucose loads with [1-²H]-glucose and U-¹³C-glucose). In both Study I and II, the plasma glucose response to the second OGTT equaled 84±2% (p=0.003) of the response to the first OGTT. Absolute insulin secretion was lower (37.8±4.3 vs 42.8±5.1 nmol.m^-2, p=0.02), but glucose potentiation (ie, higher secretion at the same glycemia) was stronger (1.08±0.02 fold vs 0.92±0.02 fold, p=0.006), the increment being higher in Study II (+36±5%) than Study I (+19±6 %, p<0.05). In pooled data, a higher glucose area during the first OGTT was associated with a higher potentiation during the second OGTT (rho=0.60, p=0.002). Neither insulin clearance nor glucose clearance differed between loads, and appearance of glucose over 3 hours totalled 60±6 g for the first load and 52±5 g for the second load (p=ns). Fasting endogenous glucose production (13.3±0.6 µmol.min^-1.kg_FFM^-1) averaged 6.0±3.8 µmol.min^-1.kg_FFM^-1 between 0-180min and 1.7±2.6 between 180-360min (p<0.03). Glucose potentiation and stronger suppression of endogenous glucose release are the main mechanisms underlying the Staub-Traugott effect.