Relative densities and massic heat capacities have been determined for the amino acids L-lysine monohydrochloride and L-arginine monohydrochloride in aqueous solution at the temperatures T = (288.15, 298.15, 313.15, and 328.15) K. These data have been used to calculate apparent molar properties which, in turn, were analyzed using extended Debye-Huckel equations to yield partial molar heat capacities C-p,m,phi(infinity) and partial molar volumes V-m,phi(infinity) at infinite dilution. The partial molar properties have been used to calculate amino acid side-chain contributions which have been compared to those values previously reported in the literature.