The partial molar volumes, V-2 degrees and partial molar heat capacities, C(p,2)degrees, determined for the tripeptides of sequence glycyl-X-glycine, where X is one of the amino acids glycine, tyrosine, glutamine, proline, and cysteine, in aqueous solution at 25 degrees C. Using these results, the partial molar heat capacities and volumes of the amino acid side chains were derived. The side chain heat capacities and volumes were compared with those obtained using other model compounds.