This study presents dispersed hold-up data for an aqueous two-phase system containing polyethylene glycol (PEG) 1500 Da and potassium phosphate (PPP) at pH 7 and 25 degrees C in a Graesser raining bucket contactor. The influences of the operational variables rotor speed and phase flow ratio on the hold-up were analyzed. Densities, viscosities and interfacial tension were measured. The results obtained were correlated by the equation proposed by Richardson and Zaki, for the description of the slip velocities. (c) 2005 Elsevier Ltd. All rights reserved.