Ultrafiltration membranes were made from bromomethylated polysulfone (BrPSf) with varying degree of substitution. They were used to bind invertase. The enzyme fixation was performed in such a way that it was incorporated within the membrane matrix. The kinetic behavior of the enzyme-loaded membranes was detd. using sucrose. The effective kinetic parameters of the reaction were obtained under diffusion-controlled and convection-controlled conditions. The diffusion expts. enabled the evaluation of the enzyme distribution within the membrane. From the balance of different educt/product ratios as a function of residence time the activity of the transferase catalyzed reaction could be derived.