Mixing enthalpies of heterocyclic compounds (THF and 1, 4-dioxane) and alpha-amino acids with a non-polar side chain (glycine, L-alanine, L-aminobutyric acid and L-valine), and dilution enthalpies of each compound have been determined in aqueous solutions at 298.15 K by a flow-mixing microcalorimeter. The heterotactic enthalpic pairwise interaction coefficients, h(xy), of each amino acid with THF and 1, 4-dioxane have been calculated by the McMillan-Mayer formalism, and discussed in terms of intermolecular interactions between the hydrated solute species. Using the additivity groups concept by Savage and Wood (SWAG), contributions of each functional group of studied solutes have been estimated. In addition, the mixing energies and Huggins parameters of amino acid-heterocyclic compound systems have been obtained by computer simulation. The results of computer simulation are consistent with enthalpic measurements. (c) 2005 Elsevier Ltd. All rights reserved.