This communication describes contact angle and swelling measurements for different (commercially available) polymeric nanofiltration membranes. Contact angle measurements and surface tension calculations on new and solvent-treated membranes confirm that organic solvents change the hydrophilicity of polymeric membrane surfaces, leading to different water permeability before and after solvent treatment. Swelling measurements confirm the assumption that a reorganisation of the membrane material takes place, leading to differences in porosity and changes in rejection. (C) 2004 Elsevier Ltd. All rights reserved.