The densities and speeds of sound in dilute aqueous solutions of the amino acids, L-asparagine, L-glutamine, L-histidine, L-aspartic acid monosodium salt, L-glutamic acid monosodium salt, L-lysine monohydrochloride, L-arginine monohydrochloride, and L-histidine monohydrochloride, were measured at (5, 15, 25, 35, and 45) degrees C. Partial molar volumes and partial molar isentropic compressibilities of these amino acids at infinite dilution were evaluated and discussed in connection with the electrostatic interactions between the charged groups of amino acid side chains and solvent water.