The transport of selected dipeptides through supported liquid membranes impregnated with di(2-ethylhexyl) phosphoric acid in n-dihexylether has been investigated. The fluxes depend on the side chain of amino acids, presence in the peptide structure. The highest fluxes were obtained for the peptides extracted with the highest efficiency. It has been found that the hydrophobicity of investigated peptides, was not the major factor, influences their SLM permeation. In the conditions studied, it has been observed that the transport of peptide-carrier complex was depending on the acidic-basic properties of the analyte. The linearly least-square fittings of log {K-1+[H+]D} and log[(HR)(2)] enable to determine the stechiometric ratio of complex formation reaction between the analysed peptide and cationic carrier D(2)EHPA. The value of the stechiometric constant (q) depends on the type (structure) of the analysed peptide. The described system allows obtaining high enrichment factors. (C) 2006 Elsevier B.V. All rights reserved.