The hydrophilicity of a regenerated cellulose (RC) ultrafiltration (UF) membrane C 30FM is a great advantage in pulp and paper mill filtration applications. However, a better knowledge on its performance stability at high pressure could increase its area of application, for instance in the sugar industry. Thus, in this study, the C 30FM was tested at different pressures from 100 to 1200 kPa in the filtration of reverse osmosis (RO) treated water, polyethylene glycol (PEG) solution and spent sulphite liquor (SSL) used in the sugar industry. In addition, the same experiments were performed with another RC UF membrane, C2, which is from another manufacturer and has its cut-off value in the same range as the C 30FM. The performances of the membranes were compared by evaluating the stabilities of membrane structure, flux and observed PEG retention. The results showed crucial differences in the compaction of the C 30FM and the C2 owing to their differences in membrane substructure. The C 30FM was more compacted than the C2 but the compaction decreased the pure water fluxes (measured at 100 kPa) of both of the membranes. The compaction did not significantly affect the observed PEG retentions of the membranes at 100 kPa. Despite the compaction both of the tested membranes were, according to the results, applicable for the filtration of SSL in the pressure range 550-750 kPa. (C) 2007 Elsevier B.V. All rights reserved.