The role of hepatovenous back-perfusion in maintaining hepatic viability was investigated during inflow occlusion (Pringle manoeuvre) of the pig liver. The study compared two ischaemia procedures of 60 min duration: hepatic inflow occlusion and inflow plus outflow occlusion (vascular exclusion). Each procedure was carried out in six pigs and liver tissue perfusion, energy metabolism, lipid peroxidation and 7-day survival were assessed. Although all pigs survived after inflow occlusion, five of six died after vascular exclusion (P < 0.01). Exclusion induced a significant decrease in perfusion to 15.3 per cent of the value before ischaemia compared with 32.4 per cent after hepatic inflow occlusion alone (P < 0.01). Although cellular adenosine 5'-triphosphate levels were significantly decreased by ischaemia in both groups, the fall was less in pigs with inflow occlusion alone (to 55 per cent of the preclamp value) than in those with exclusion (to 24 per cent of the preclamp value) (P < 0.01). The plasma phosphatidylcholine hydroperoxide level rose immediately after reperfusion in pigs with exclusion, while the level remained constant after inflow occlusion alone. There is a fundamental difference between the two ischaemia procedures: back-perfusion from the vena cava contributes to the maintenance of liver function during inflow occlusion.