Variations in blood flow to different sinusoids within the liver can prevent uniform uptake of solutes from plasma and contribute to cellular ischemia in low-flow states. However, the degree of variability and the role of hepatic artery perfusion in maintaining uniform flow are poorly defined. We used an indicator dilution technique to compare the distribution of sinusoidal transit times in isolated rat livers perfused through the portal vein alone with livers perfused using both portal vein and hepatic artery. Physiological flow rates were used in each case (1.2 +/- 0.3 ml.min-1.g liver-1), but the second group received 32% of flow through the hepatic artery. Intralobular flow heterogeneity was further assessed by gamma counting of small (approximately 100 mg) pieces of the liver after bolus injection of approximately 5 mCi of a highly extracted compound ([125I])triiodothyronine) into the portal vein. Hepatic artery perfusion had no significant effect on mean sinusoidal transit time or intrahepatic distribution volume for 51Cr-labeled red blood cells or 125I-albumin. Analysis of the outflow profiles indicated that hepatic artery perfusion did not affect transit time dispersion. However, heterogeneity of flow to individual portions of the liver, measured as the coefficient of variation, increased from 19 to 30%. These results indicate relatively uniform perfusion of the sinusoids in the portally perfused rat liver and that additional perfusion of the hepatic artery does not further improve hemodynamics. These results have significance for the design and interpretation of transport studies with the use of the perfused rat liver model.