Rat hepatocytes were cultured in three polysulfone, hollow-fiber cartridges, characterized by two membrane variables: pore size and inner diameter (ID). Hepatocytes entrapped in a micro-filtration (MF) cartridge with the membrane pore size 0.1 microm had twice the production of urea and 4-fold the amount of albumin in comparison to the control cartridge, a ultra-filtration (UF) cartridge with a molecular weight cut-off (MWCO) of 100 kDa. Hepatocytes entrapped in a UF cartridge with ID of 0.5 mm secreted twice the amount of urea and 10-fold the amount of albumin compared with the control UF cartridge.