Whether laser-Doppler flowmetry can be used to monitor liver blood flow was evaluated in a porcine model in which portal venous blood flow was followed indirectly by electromagnetic flowmetry applied to the superior mesenteric artery, and total hepatic venous outflow was measured directly by using an extracorporeal circuit. Hepatic venous outflow at rest was 23.5 +/- 5.7 ml.kg body wt-1.min-1. Occlusion of the hepatic arterial supply reduced hepatic laser-Doppler blood flow to 22%, but hepatic venous outflow only to 80%. Portal venous blood flow remained unchanged or increased slightly. Occlusion of the portal vein, on the other hand, decreased hepatic laser-Doppler blood flow values to 37% and hepatic venous outflow to 13%. Increased hepatic venous outflow pressure, caused by a positive end-expiratory pressure or elevation of the draining cannula, reduced flow and caused approximately equal changes in the three variables, as did reduced flow by step-wise bleeding. From these experiments in the pig it is concluded that laser-Doppler flowmetry on the liver surface clearly reflects relative changes of the total liver blood flow, as exemplified in this study, during venous stasis and bleeding. The technique is, however, more sensitive to blood flow changes in the hepatic artery as compared with the portal vein.