Extractive ultrafiltration of a-phenylglycine from sodium hydroxide solutions with the ion-exchange extractant trialkylmethylammonium chloride (TOMACl) dissolved in toluene using a microporous polypropylene hollow fiber contactor has been studied. The effect of the hydrodynamic conditions on the mass-transfer rates was determined. The overall mass-transfer coefficients were calculated by two different methods, i.e. assuming a constant distribution coefficient and using an equilibrium model. Individual mass-transfer coefficients were estimated by two alternative methods: Wilson-plot two-step calculation, and a more accurate one-step calculation. It is shown that a correct equilibrium model is required for the estimation of the mass-transfer coefficients. The influence of feed concentration, flow pattern and the composition of the stripping solution on the extractive ultrafiltration performance is also reported. (c) 2004 Published by Elsevier B.V.