Host-guest interactions have been widely employed in various techniques in biochemistry in the last decades. In this way, the use of calix[6]arenes modified with a carboxylic acid as host in the host-guest extraction of immunoglobulin G (IgG) is studied. it is possible to extract IgG from an aqueous medium. Different operational parameters such as pH, salt concentration and stirring speed were evaluated. At high pH, up to 50% of the IgG can be transferred to the organic phase. The study of pH demonstrates that the interaction mechanism depends on a proton exchange mechanism together with hydrogen-bonding. Salt concentration has a direct effect on the interaction strength of the lysine residues of IgG and the calix[6]arene, leading to a diminished extraction at high salt concentrations. For the prevention of denaturation the contact mode and intensity of mixing are crucial. Based on the data obtained from kinetic and equilibrium studies a suggestion for the extraction mechanism is made. (C) 2008 Published by Elsevier B.V.