The extraction of lysozyme from aqueous solutions through a flat-sheet microporous membrane (pore size 0.45 mu m, thickness 147 mu m, porosity 0.75) into an isooctane solution of sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelles was examined. Batch liquid-liquid extraction experiments were first conducted at different lysozyme concentrations (250-1000 mg L-1), KCl concentrations (0.1-1.2 M), pH (2-12) and AOT concentrations (0.01-0.1 M) to obtain equilibrium relationships. Effective extraction of lysozyme was achieved in the KCl concentration range of 0.1-0.4 M and pH range of 4-9. More than 90% of lysozyme could be stripped to an aqueous phase of high alkalinity (pH 11.5) and high KCl concentration (1.5 M). A mass transfer model was proposed that considers all diffusion in the aqueous stagnant layer, membrane and reverse micellar stagnant layer to predict the transport flux of lysozyme in the present membrane-based extraction process. The solubilization of lysozyme from aqueous phase to the AOT/isooctane reverse micelles was assumed to attain equilibrium instantaneously. A good agreement between the calculated and measured fluxes was obtained under the ranges studied (standard deviation, 11%). (c) 2006 Elsevier B.V. All rights reserved.