The effects of arterial-portal glucose difference on the gluconeogenesis from lactate were studied using the bivascular perfused liver isolated from the fasted rat. The liver was cyclically perfused at flow rates of 14 ml/min from the portal vein and of 7 ml/min from the hepatic artery with the total volume of 35 ml of perfusion medium containing 2 mM glucose, 3 mM lactate and (U-14C)-lactate for 20 min. Glucose was infused at a rate of 27.75 mumol/min into the arterial cannula (A-experiment) or the portal cannula (P-experiment), making each arterial-portal glucose gradient of +3.96 mM (arterial glucose > portal glucose) and -1.98 mM (arterial glucose < portal glucose) throughout the experiment. Perfusate lactate concentration was lower in A-experiment than in P-experiment (1.40 +/- 0.25 vs 1.93 +/- 0.23 mM at 20 min, mean +/- SD, p < 0.05). Incorporation of radioactivity from (U-14C)-lactate into glucose carbon 1 in perfusate was 5.7 +/- 0.8% of total radioactivity per 20 min in A-experiment vs 2.8 +/- 0.6%/20 min in P-experiment (p < 0.01). These results suggest that the arterial-portal glucose difference is an important factor to regulate the hepatic gluconeogenesis.