We describe a method for evaluating the apparent molar thermodynamic characteristics of solutes using data derived from ultrasonic velocity measurements. Using this method, we have determined the apparent molar volumes, the apparent molar thermal expansibilities, the apparent molar heat capacities, and the apparent molar adiabatic and isothermal compressibilities of glycine and alanine in aqueous solutions over the pressure and temperatures ranges of 1-1000 bar and 18-45-degrees-C, respectively. We interpret the resulting data in terms of a temperature and pressure induced reduction in the hydration of the charged termini. Thus, at elevated temperatures and pressures, water in the bulk medium becomes more like water in the hydration shell of the charged groups.