The effect of two commonly used sterilization methods for artificial kidneys on the morphology and performance of hollow fiber Hemophan® hemodialysis membranes was studied. A relatively new membrane characterization method, thermoporometry, was used to determine the pore size distributions and porosities of the differently treated membrane samples. The samples used for this study were not treated with a concentrated glycerol solution before sterilization. Hemophan was found to have a pore size distribution with pore radii between 1.5 and 12 nm, the volume porosity was 20%. The sample sterilized with ethylene oxide (EtO) had a volume porosity of 18% which was due to a decrease of the pore volume of the smallest pores. The applied dry steam sterilization treatment resulted in a drastic collapse of the large pores while smaller pores were formed. The calculated porosity was only 10%. The `tortuous capillary pore model¿ was used to predict the performance of the artificial kidneys from the pore size distribution in the membrane material. In vitro dialysis experiments with creatinine and vitamin B12 were carried out to compare the calculated and measured clearance rates. Also the ultrafiltration capacity of the devices was determined. It was found that a reasonable estimation of the ultrafiltration capacity could be made. The calculated clearance rates were systematically underestimated, although the relative dependence of the clearance rates on the applied sterilization methods was approximated reasonably.