Glucose is absent from human bile and present in low concentrations in bile from the rat. To study the mechanisms of this blood-bile glucose concentration difference, infusions of glucose were administered i.v. to 300-400 g male Sprague-Dawley rats with ligated renal pedicles and to two postcholecystectomy patients with indwelling t-tubes. Glucose was assayed in plasma, bile, and rat liver by a hexokinase method specific for D-glucose. In man, glucose was detected in bile when plasma glucose increased above 350 mg/100 ml. In animals studies, low concentrations of bile glucose were observed at plasma levels between 100 and 300 mg/100 ml. However, when plasma concentrations increased between 400 and 900 mg/100 ml, glucose appeared more rapidly in bile, defining by extrapolation an apparent plasma glucose threshold of 280 mg/100 ml. Intraportal phlorizin, a competitive inhibitor of glucose transport, significantly increased bile glucose concentrations. Plasma-bile concentration differences were also observed in rats after i.v. [3-14C]O-methyl glucose (3-O-MG) but not after [3H]mannitol. Hepatic glucose levels were never lower than plasma levels and liver-plasma 3-O-MG ratios were 0.92 +/- 0.22 indicating that entry of glucose and 3-O-MG into hepatocyte water was not limiting. Furthermore, when sodium dehydrocholate augmented canalicular secretion, biliary glucose excretion increased proportionally suggesting that glucose entry into bile was not impeded. When estimates of hepatic glucose secretion were compared with biliary glucose excretion, the latter increased progressively when estimated secretion rates exceeded 50 micrograms/min or when phlorizin was given. Finally, during bile stop-flow experiments, [3-14C]O-MG and [14C]glucose were selectively removed from bile compared with [3H]mannitol. The findings suggest that glucose and 3-O-MG are reabsorbed from bile after entry at the hepatocyte, accounting for their low bile-plasma ratio. The biliary glucose transport process may be described by Michaelis-Menten kinetics and is analogous to recently defined kinetics for renal tubular reabsorption of glucose. These studies provide evidence that certain products of bile secretion may undergo a "biliohepatic" circulation.