This paper reports a comprehensive experimental investigation, utilizing ultrasonic techniques to study the kinetics of proton‐transfer reactions in nondilute aqueous solutions of amino acids. Ultrasonic absorption and velocity measurements in the range of frequencies 10–130 MHz and ofpH 0.96–11.6 are analyzed in terms of single relaxation behavior. Activity coefficients are calculated by three methods; the method based upon standard ionic radii and the mean dielectric constant of the solutions is found to yield the most acceptable estimates. The dependencies of rate constants upon initial concentration of solute, ionic strength, and temperature are displayed in the range 0.25M–1.0M, 0.25M–1.0M, and 22°–37°C, respectively. It is concluded that proton‐transfer reactions at amino and carboxyl groups cannot be responsible for significant contributions to the total ultrasonic absorption coefficient of blood in the physiological range ofpH.