The hepatic disposition characteristics of recombinant human interleukin-ll (rhIL-11) were investigated in perfused rat liver to clarify the mechanism of hepatic clearance which is a major contributor to the rapid clearance of rhIL-11 in vivo. We analyzed the disposition characteristics of [In-111]-labeled rhIL-11 using a single-pass constant infusion mode at different concentrations of rhIL-11, The venous outflow: rapidly reached a steady-state condition at every concentration. Liver extraction ratio at steady-state (E-ss) was decreased with increase in the concentration, suggesting that there is a saturable interaction between the liver cells and rhIL-11 molecule. Cellular localization experiments demonstrated that rhIL-11 was taken up by both liver parenchymal and nonparenchymal cells depending on their surface area, suggesting that this uptake was mediated by electrostatic interaction due to cationic charges in the cytokine.