Liquors from the aqueous processing of Eucalyptus wood were diafiltered through a nanofiltration ceramic membrane, and experimental data concerning the time-course of flux and concentrations of the different compounds present in the medium (monosaccharides, oligosaccharides, oligosaccharide substituents and other non-volatile compounds) were determined. A mathematical model based on a combination of osmotic pressure and an additional in-series resistance provided a quantitative interpretation of experimental data. (C) 2009 Elsevier B.V. All rights reserved.