Enthalpies of mixing in aqueous solutions Of L-valine and L-threonine with pyridine and methylpyridine isomers and their enthalpies of dilution have been determined by flow microcalorimetry at 298.15 K. The results have been analyzed using the excess function concept, and heterotactic enthalpic pairwise interaction coefficients, h(xy), of the virial expansion of the excess enthalpy have been obtained. These are briefly discussed in terms of intermolecular interactions between the hydrated solute species. In addition, the results obtained in the present paper along with literature data have been treated in terms of the Savage-Wood additivity group (SWAG), and values of the functional group interaction parameters for a-amino acids + pyridine and alpha-amino acids + methylpyridine systems have been estimated. The SWAG approach has been appraised in terms of the results obtained.