Relative densities rho-rho (0) have been measured over an extended concentration range for aqueous solutions of glycylglycine and L-Serine in the temperature range 298 less than or equal to (T/K) less than or equal to 423 and the pressure range 0.10 less than or equal to (p/MPa) less than or equal to 30.00. Apparent molar volumes V-m,V-phi have been calculated from measured densities and have been used to estimate partial molar volumes at infinite dilution V-0. Values of V-0 obtained for aqueous solutions of L-serine in water have been combined with previously reported V-0 values for aqueous solutions of glycine, to obtain estimates of serine side chain contributions to partial molar volumes over an extended temperature and pressure range. The reported volumetric data of glycylglycine have been used to calculate the partial molar volume change associated with the formation of a peptide bond.