The recovery and purification of lysozyme from lien egg white has been investigated in an aqueous two-phase systems composed of thermoseparating random copolymers of ethylene oxide (EO), propylene oxide (PO) and potassium phosphate. In the primary extraction step lysozyme was satisfactorily partitioned to the top polymer-rich phase in a system composed of 40% (w/w) EO50PO50, 10% (w/w) potassium phosphate, and 0.85 M sodium chloride at pH 9.0. diluted 3-fold with crude egg white, where contaminating proteins were discarded in the bottom phosphate-rich phase. After the primary phase separation the upper EO50PO50 phase was removed and subjected to temperature-induced (65 degrees C) phase separation, which resulted in the partitioning of pure lysozyme to the top water phase. The separation system was found to be efficient in achieving the purification of lysozyme in a high yield of 85% and specific activity of 32,300 U/mg of protein, with a purification factor of 16.9 and a concentration of lysozyme in the water phase of 2.3 g/l in two extraction steps. (C) 2009 Elsevier Ltd. All rights reserved.