This article presents a method for evaluating the intrinsic kinetic parameters of the specific substrate utilization rate (r) equation and discusses the results obtained for anaerobic sludge-bed samples taken from a horizontalflow anaerobic immobilized sludge (HAIS) reactor. This method utilizes a differential reactor filled with polyurethane foam matrices containing immobilized anaerobic sludge which is subjected to a range of feeding substrate flow rates. The range of liquid superficial velocities thus obtained are used for generating data of observed specific substrate utilization rates (r obs ) under a diversity of external mass transfer resistance conditions. The r obs curves are then adjusted to permit their extrapolation for the condition of no external mass transfer resistance, and the values determined are used as a test for the condition of absence of limitation of internal mass transfer. The intrinsic parameters r max , the maximum specific substrate utilization rate, and K S , the half-velocity coefficient, are evaluated from the r values under no external mass transfer resistance and no internal mass transfer limitation. The application of such a method for anaerobic sludge immobilized in polyurethane foam particles treating a glucose substrate at 30ยฐC resulted in intrinsic r max and K S , respectively, of 0.330 mg chemical oxygen demand (COD) โข mg -1 volatile suspended solids (VSS) โข h -1 and 72 mg COD โข L -1 . In comparison with the values found in the literature, intrinsic r max is significantly high and intrinsic K S is relatively low.