Liquid-liquid displacement porosimetry (LLDP) has been used to analyse very regular track-etched polymeric membranes in the ultrafiltration (UF) range, with a nominal pore diameter of 50 nm. A fully automated porosimeter has been used in the evaluation of pore size distributions and results have been compared with image analysis performed on scanning electron micrographs (SEM-CIA) of the membranes. Comparison gives a nice agreement between both results (mean pore radius of 23.6 nm for LLDP results and 24.0 nm for SEM-CIA performed on the same samples used for LLDP). A not so satisfactory agreement is obtained for other indirectly evaluated parameters as porosity (means of 1.4 and 2.1%) or the mean total number of pores (19.6 x 10(12) pores/m(2), from LLDP and 11.1 x 10(12) pores/m(2) for SEM-CIA). These results show that LLDP measurements have good accuracy and reproducibility and that the analysing fluid mixtures used do not significantly modify neither the chemical nature nor the structure of the membrane material used. Of course, ulterior research should be made in order to elucidate the influence of solvents and other parameters of the LLDP analysis. Membranes so regular as track-etched UF ones could be used as appropriate standards to refine the technical parameters for LLDP. (C) 2004 Published by Elsevier B.V.