The hepatic extraction, metabolism, and biliary excretion of doxorubicin (DX) were studied in the isolated perfused rat liver. Three doses of DX equivalent to 2, 20, and 100 mg/kg in rats were studied over a period of 3 h after bolus injection into the reservoir. DX and metabolites concentration in perfusate, bile, and liver were determined by high-pressure liquid chromatography. The hepatic extraction ratio was low (less than 0.24) and decreased progressively over the 3 h. The hepatic extraction and clearance were significantly lower at the highest dose. Doxorubicinol (DX-OL) was the only metabolite detected in the perfusate, accounting for less than 4% of the total AUC. Thirty-one to thirty-three percent of the dose was excreted into bile over 3 h as unchanged DX. This was reduced to 22% at the highest dose. Only 0.35%-1.33% of the dose was excreted as DX-OL. DX aglycones were found only in the liver, where they represented 20%-30% of the total fluorescence at 3 h. In conclusion, in this model DX has a low extraction ratio, is poorly metabolized and extensively excreted into bile.