In this work the modified Wilson equation, proposed in a previous publication, for aqueous binary polymer solutions is extended to calculate liquid-liquid equilibrium of aqueous two-phase systems containing one salt with either polyethylene glycol or ethylene oxide-propylene oxide random copolymer. The Debye-Huckel equation based on the Fowler-Guggenheim theory is used to represent the long-range electrostatic interactions of ions. The parameters are estimated from only one or two tie-lines and are used to predict the phase diagrams with different molecular weights and polymer-salt systems at different temperatures. The predictions obtained with the modified Wilson equation are in good agreement with the experimental data. (C) 2004 Elsevier Ltd. All rights reserved.