This work evaluates the use of room temperature ionic liquids (RTILs) in liquid membranes. Water possesses non-negligible solubility in room temperature ionic liquids, despite the fact that the latter may be water immiscible. This prompted us to study the potential role that water may play on the mechanism of solute transport between aqueous phases, separated by a supported liquid membrane with ionic liquids. Amino acids were chosen as case-study solutes and the role played by water in their mechanism of transport was evaluated. The assessment of the transport mechanism of amino acid derivatives, with potentially different affinities towards the RTILs is also of interest. As the liquid-liquid extraction of amino acids by RTILs is potentially lower than that of amino acid esters, given the fact that the latter are more hydrophobic due to the substitution of the acidic proton of amino acids by an alkyl group, amino acid esters were also selected for study. (C) 2004 Elsevier B.V. All rights reserved.