An in vivo method of isolated rat liver perfusion was developed with true vascular isolation and recirculating perfusate. This new surgical technique to temporarily isolate the liver vascularly, and the perfusion procedure are described in depth. Twelve inbred WAG/RIJ rats were subjected to 25 min of normothermic liver perfusion without chemotherapy, and all rats survived the procedure. Hepatic functional and histological integrity were not significantly altered during perfusion. To determine the role of isolated liver perfusion (ILP) as a means of improved targeting of antitumor agents, 5-fluorouracil (5-FU) concentrations were monitored in hepatic tumor and liver tissues and in systemic plasma using high-performance liquid chromatography. Fifty-one rats with hepatic tumors of colonic origin were randomly assigned to one of three dosage groups (20, 40, or 80 mg/kg) receiving 5-FU by ILP, hepatic artery infusion (HAI), or jugular vein infusion (JVI). ILP resulted in significantly increased 5-FU concentrations in liver tissue. However, no significant differences were found in tumor tissue concentrations of 5-FU between the three treatment modalities. 5-FU concentrations in tumor tissue increased as a function of the dose with ILP, HAI, and JVI. ILP was associated with the lowest systemic drug concentrations. The low systemic 5-FU concentrations with ILP suggest a higher maximum tolerable dose. This mode of treatment deserves to be studied further in our model before conclusions can be drawn regarding its therapeutic potential.