The adsorption of phenylalanine, aspartic acid, asparagine and aspartame from phosphate-buffered aqueous solutions with modified divinyl-benzene-polystyrene resins has been investigated using high pressure liquid chromatography (HPLC). The pH studied was 2.8, the temperature range was 293-313 K and the ionic strength was maintained at 1.0 mol dm-3. Over the range of variables investigated, the adsorption isotherms are linear and may be characterized by temperature and pH-dependent apparent adsorption equilibrium constants, characteristic of the resin-adsorbate system. By studying the dependence on temperature of this adsorption constant, heats of adsorption and entropy of adsorption have been estimated. In terms of the heat liberated on adsorption, the amino acids and a dipeptide can be ranked thus: aspartame > phenylalanine > aspartic acid > asparagine.