The extraction of amino acids (tryptophan (Trp), phenylalanine (Phe) and dipeptides (tryptophan-leucine (Trp-Leu), phenylalanine-leucine (Phe-Leu)) is examined by passing a "feed" solution (an aqueous solution containing any of the target solutes) through the fiber-side of an extra-flow hollow-fiber membrane module (HFMM). The membrane module (2.5 cm diameter x 20 cm long) has a shell-and-tube configuration and allows flow of two solutions in the fiber and shell sides. The extraction solution contained an ionic carrier, Aerosol OT (AOT), dissolved in a solvent, oleyl alcohol. The feed and organic solutions were circulated on the fiber side and shell side, respectively. The target solute (any of the amino acids or peptides) diffuses to the interface, forms a complex with the carrier; the carrier-solute complex is transported to the shell side, where it can be recovered. A mathematical model that includes the equilibrium distribution at the interfaces and the convective flow in the module is presented. A straightforward use of the experimental data has been shown to be able to calculate the overall mass transfer coefficient of the extraction process. The value of the overall mass transfer coefficient is similar to those in the literature and has been found to be significantly affected by the solute type and feed solution pH. (C) 2004 Elsevier B.V. All rights reserved.