A frequency response technique is applied to the study of mass transfer in liquid-phase adsorption on polymeric adsorbents. The technique uses an imposed sinusoidal temperature cycle to elicit an adsorbate concentration response in a stirred vessel. Mass transfer parameters (intraparticle diffusivities and film coefficient) are obtained from the steady periodic concentration response by matching experimental phase angle lag and amplitude ratio to model predictions. The technique is applied to the adsorption of the amino acids phenylalanine and tryptophan from aqueous solution onto two commercial polymeric adsorbents with varying pore size. In all cases, the technique yields results that are consistent with the behavior observed in isothermal batch uptake experiments with a finite concentration step. However, the frequency response technique is found to provide the advantage of yielding mass transfer parameters for near equilibrium conditions and of detecting deviations from Fickian diffusion behavior, such as the presence of surface barriers.