The possible contribution of hepatocellular damage and portal-systemic shunting to hyperinsulinism in cirrhosis was studied in 23 cirrhotics, 8 of whom had a surgical portacaval shunt, and 16 controls by measuring insulin and the connecting peptide (C-peptide) concentrations in simultaneous samples of peripheral arterial and hepatic venous blood. The fractional hepatic insulin extraction (0.48 +/- 0.06, mean +/- SE) was normal in cirrhosis. The hepatic insulin elimination rate was directly related to arterial insulin levels (r = 0.91, P less than 0.001) even at very high circulating levels. Extrahepatic insulin metabolism was measured across the kidney and lower limb. There were no significant differences between cirrhotics and control subjects in relation to renal (0.25 +/- 0.05 vs. 0.23 +/- 0.04) and lower limb insulin extraction (0.14 +/- 0.07 vs. 0.19 +/- 0.04). While in the control group hepatic venous insulin (0.143 +/- 0.018 pmol/ml) markedly exceeded the peripheral insulin concentration (0.083 +/- 0.009 pmol/ml, P less than 0.01), the contrary was found in cirrhotics with end-to-side portacaval shunt in whom all the pancreatic venous effluent is shunted to the systemic circulation (hepatic venous insulin, 0.130 +/- 0.028 pmol/ml; peripheral, 0.234 +/- 0.037 pmol/ml; P less than 0.01). Portal-hypertensive cirrhotics without a surgical portacaval shunt also had hepatic venous insulin levels (0.132 +/- 0.029 pmol/ml) below peripheral arterial insulin concentrations (0.205 +/- 0.041 pmol/ml, P less than 0.01). The study suggests that hyperinsulinism in cirrhosis is not the result of an intrinsic defect of hepatic insulin metabolism but of the spontaneous shunting of portal blood to the systemic circulation.