New TiO2-NF membranes with a mean pore size of 0.9 nm and a cut-off of 450 D were tested in decolouring of textile waste water. A pilot plant with a membrane area of 5.1 m(2) was integrated in the textile finishing in order to treat only the coloured parts of the waste water near the colouring and washing machines and to recycle the hot permeate as process water. The pilot plant was tested with 30 types of different coloured waste water over a period of 6 weeks to detect optimal parameters for the filtration process with a focus on high flux and low running costs. Due to the differences in the composition of the dyes a decolouring of 70-100% was obtained. The fluxes varied between 0.2 and 1.1 m(3)/h, whereas the running costs were 0.50-2.80 DM/m(3) permeate, respectively.