Hepatocyte based artificial liver support systems are under investigation to support acute liver failure patients. The main purpose of such systems is to serve as a bridge to liver transplantation, or to promote spontaneous liver recovery. Limitation in mass-transfer capacity makes hollow-fiber bioreactors unsuited for long-term functioning of hybrid devices. We developed a novel radial-flow bioreactor in which the fluid perfuses the module from the center to the periphery, after having diffused through a space occupied by a threedimensional structure filled with the hepatocytes. Five grams of freshly isolated porcine hepatocytes were seeded into uncoated, woven-non woven, hydrophilic polyester fabric, overlaid by two polyethersulfone membranes. Liver cells were perfused with 37° C-warm, oxygenated, serum-free tissue culture medium, in which NH4Cl and Lidocaine were added at the final concentration of 1 mM and 60 µ g/ml, respectively. Ammonium chloride removal, urea synthesis, monoethylglycinexylide (MEGX), pO2, pCO2, and pH were measured throughout the 14 day duration of the study. In a separate set of esperiments, a scaled-up version of the radial flow bioreactor containing 150 grams of cells was perfused for 7 h with recirculating human plasma and MEGX production was monitored. During the 2 weeks of the study, an increasing production of urea was paralleled by constant ammonium removal. MEGX concentration after Lidocaine addition increased throughout the 14 days of perfusion with tissue culture medium, as well as after 7 hour perfusion with human plasma. Under transmission and scanning electron microscopy cells appeared attached to the polyester and one to each other, displaying ultrastructural features typical of functioning hepatocytes. Our study showed that liver cells were metabolically active when perfused into the radial-flow bioreactor. This configuration allowed close contact between media, or plasma, and cells at a physiological flow rate, by equalizing the concentration of the perfusing components, including O2, throughout the module. Our results suggest a potential use of this system for temporary extracorporeal liver support in acute hepatic failure patients.