Glucose oxidase (GOD) and catalase (CAT) were chemically immobilized onto three types of ultrafiltration polyacrylonitrile membranes with increase pore sizes (PAN 1-PAN 3) and one microfiltration polyamide membrane. The initial membranes were modified to generate amino and amide groups on their surface, necessary for the covalent immobilization of the enzymes. The diffusivity parameter of glucose through the initial and modified membranes was determined. It was found out that the glucose diffusion, increased with the increase of the pore size. The slight increase of glucose diffusion parameters was observed for the modified membranes in comparison with the initial membranes. The diffusivity of glucose through the inactivated enzyme membranes was determined also. A minor decrease in the values of these parameters with respect to glucose was observed for the enzyme PAN 2 membrane, while for the PAN 3 and PA enzyme membrane there was two-fold decrease in the obtained parameter values (compared to the initial and modified membranes). There was no significant change in the values of the indicated parameters with respect to H2O2 for different modified and enzyme membranes. The mass transfer coefficients (K-L), thickness of boundary layer (delta), Sherwood number (Sh) and Thiele modulus (phi) as well as their influence on the efficiency of the enzyme couple GOD-CAT immobilized onto different pore size polymer membranes were also studied. The final results showed that the two immobilized systems with PAN 3 and PA membranes, as carriers were effective as compared to PAN 1 and PAN 2 membranes. (c) 2006 Elsevier Inc. All rights reserved.