Abstract Nanofiltration has two interesting features: 1. - a fractionation capacity for different organic components in aqueous solutions, the ‘cut-off’ being in the range of 300 kg/kmol molecular weight 2. - the potential of realizing the Donnan-effect with respect to anions of different valency. Promising areas of application are cases where • - a high rejection for single-valent salts is not required or even unwanted • - a separation of anions of different valency must be achieved • - fractionation of high and low molecular weight organics is required Systematic experiments concerning the fractionation of different organics in aqueous solutions like amino acids or solvents are carried out by the Institut für Verfahrenstechnik of Aachen Technical University. Hopefully these experiments will result in • - relationships describing material transport in nanofiltration membranes • - a broad knowledge of separation problems which can be solved economically by nanofiltration — alone or in combination with other separation processes.