Using in situ perfused rat liver-pancreas preparations, the hepatic clearance of biphasically released endogenous insulin was studied using livers of fed and fasted rats. Hepatic insulin extraction was determined by subtracting the mean endogenous insulin output found in the posthepatic vena cava effluent of liver pancreas preparations from the amount of insulin found in the prehepatic portal effluent of perfused pancreas preparations. All pancreas perfusions and liver-pancreas perfusions were subjected to the same plasma glucose stimulus (250 mg/dl) for 40 min. In the fed state, no significant hepatic extraction of insulin occurred. The biphasic pattern of insulin appearance in the posthepatic vena cava effluent, which ranged from less than 1 to 21 ng/ml, was unaffected by passage through the liver. In contrast, when rats were fasted for 24 h, approximately 50% of the insulin released into the portal vein was removed by their livers during one transhepatic passage. After a 48-h fast, insulin extraction capacity decreased relative to the capacity observed for livers of 24-h fasted rats.