Sound speeds have been measured for aqueous solutions of six tripeptides of sequence glycyl-X-glycine, where X is one of the amino acids glycine, alanine, leucine, asparagine, threonine, and tyrosine at T = 298.15 K and at the pressures p = (10, 20, 40, 60, 80, 100, and 120) MPa. Using methods described in previous work, these sound speeds were used to derive the partial molar volumes at infinite dilution, V-2(o), the partial molar isentropic compressions at infinite dilution, K-S,2(o), and the partial molar isothermal compressions at infinite dilution, K-T,2(o) {K-T,2(o) = (partial derivative V-2(o)/partial derivative p)(T)}, for the tripeptides in aqueous solution at the elevated pressures. The results were used to calculate the partial molar volumes and partial molar isothermal compressions for the various amino acid side-chains over the pressure range p = (10-120) MPa. (C) 2016 Elsevier Ltd. All rights reserved.