Viscosity values of l-histidine/l-glutamic acid/l-tryptophan/glycylglycine + 2 M aqueous KCl/KNO 3 solutions have been determined experimentally as a function of molal concentration of amino acid/peptide at different temperatures: (298.15, 303.15, 308.15, 313.15, 318.15, and 323.15) K. Using the viscosity values of the solvent and solution, the relative viscosity, specific viscosity, and viscosity B-coefficient values have been computed. The trends of the variation of experimental and computed parameters with the solute concentration and temperature have been interpreted in terms of zwitterions-ions, zwitterions-water dipoles, ions-water dipoles, and ions-ions interactions operative in the systems.