The coloured effluents from pulp and paper mill industry are treated anaerobically and/or aerobically by a two stage membrane system with high efficiency. Three different types of membranes (UF and RO (BW and SW)) were used in the experiments. Surface area of each membrane was 2 m(2). The combination of ultrafiltration (UF) and reverse osmosis (RO) treatment achieve a very high removals of COD (98-99%), colour and conductivity. At the end of a single pass with RO using seawater (SW) membrane, the initial GOD, colour and conductivity values were reduced to 10-20 mg/l, 0-100 Pt-Co units and 200-300 mu s/cm, respectively. The influent, UF permeate, RO permeates for brackish water (BW) and seawater (SW) membranes were 6000-6700 mu s/cm 5500-5900 mu s/cm 1000-1500 mu s/cm and 200-300 mu s/cm respectively. Excellent conductivity rejections were obtained in the UF and RO membrane systems. Almost complete colour removals were achieved in the RO experiments with SW membranes. RO studies with BW membranes were also performed with the same permeate from the first stage UF study. The observed flux has declined with time and membranes were cleaned periodically to maintain a constant flux. Applying this advanced membrane treatment technology, it is clear that about 60 percent of the process water can be recycled in the investigated industry. (C) 1999 IAWQ Published by Elsevier Science Ltd. All rights reserved.