The effects of hepatic nerve stimulation, norepinephrine and 6-hydroxydopamine (6-OHDA) on hepatic hemodynamics were investigated in rat livers perfused in situ via both the portal vein and hepatic artery. Nerve stimulation caused a significant fall in total liver blood flow and an increase in portal and arterial pressures. Norepinephrine and 6-OHDA in addition to causing a fall in flow caused significant pressure increases in the bed perfused (arterial or portal). Under basal conditions, the inter- and intra-lobar distribution of microspheres (113Sn- or 57Co-labelled) introduced via the portal vein or via the hepatic artery was homogeneous in all 6 liver lobes. During nerve stimulation, homogeneity of interlobular microsphere distribution was maintained. However, the intralobar distribution of microspheres introduced via the portal vein displayed a significant redistribution from the periphery to the core of each of the four largest lobes studied (p < 0.05). In contrast, when microspheres were introduced via the hepatic artery, there was no universal redistribution of microspheres with only one lobe demonstrating a significant decrease in flow to the periphery (p > 0.05). Infusion of norepinephrine (10(-8) M) or 6-OHDA (1 mg.kg-1 body weight) via either the hepatic artery or the portal vein was without effect on the intrahepatic distribution of the microspheres. We conclude from our results that during hepatic nerve stimulation there is a significant redistribution of portal venous but not hepatic arterial flow from the periphery to the core of the liver lobe. The persistence of hepatic arterial flow during nerve stimulation may represent a protective mechanism by which the periphery of the liver, especially the bile ducts, remains perfused during a reduction in total liver blood flow.