An organic ultrafiltration membrane in polyethersulfone is employed in the present study for the removal of cupric ions, complexed beforehand on poly (vinyl alcohol), from aqueous solutions. The rejection of the complexed metal ions is highlighted by means of viscometric and UV-vis spectroscopic analysis of the feed solutions and the ultrafiltrates. The considered parameters are, in particular: (a) the pressure: the results obtained show that the variation of the pressure acts on the flow without affecting the rejection rate. Indeed, whatever the value of the applied pressure, the macrocomplex is completely rejected when the formation conditions of the macrocomplex are met. (b) The pH: the rejection rate becomes more significant as the formation pH of the complex is approached and reaches a maximum in the pH range above 7.0 and the UV-vis spectra of feed solutions for several pH show clearly that it is well in this field of pH that the macrocomplex is formed. (c) The relative concentration of the reacting species: the maximum of rejection is reached, at the pH formation of the macrocomplex, for a concentration of poly(vinyl alcohol) of 1.5 g/L when the metal solution to treat is at the concentration of 5 x 10(-4) M. (c) 2007 Elsevier B.V. All rights reserved.