Apparent molar heat capacities have been determined for aqueous solutions of glycine at temperatures from 352.09 K to 470.63 K and glycylglycine at temperatures from 352.09 K to 423.15 K. Both systems were investigated at a pressure of 10.0 Mpa. Measurements were performed with a differential flow calorimeter that is capable of operation at temperatures > 723 K and pressures to approximately 40.0 MPa. Partial molar heat capacities at infinite dilution have been calculated from apparent molar values and have been corrected for "relaxation" contributions. The reported partial molar heat capacity values for aqueous glycine and glycylglycine solutions have been modelled using the revised Helgeson, Kirkham, and Flowers semi-empirical equations of state. These models for solutions of glycine and glycylglycine in water have been compared with those previously reported in the literature.