The procedure, which enables to determine the basic transport properties of membrane/solution systems on the basis of the measurement in a continuous dialyzer at steady state, has been elaborated. The determination of these characteristics is based on the numerical integration of the set of differential equations describing the concentration profiles in both compartments of the dialyzer followed by the optimizing procedure. The model used takes into account changes in flow of liquid along the membrane in both compartments as a consequence of the solvent flow through the membrane. Using the procedure mentioned above, the overall dialysis coefficient, permeability of the membrane and the membrane mass transfer coefficient have been determined for the Neosepta-AFN membrane/sulfuric acid system. (c) 2006 Elsevier B.V. All rights reserved.