The equilibrium and mass transfer rates of phenylalanine in cation-exchange resins with different nominal degree of crosslinking are determined at temperatures in the range 5-85 degrees C. The equilibrium uptake is found to be relatively insensitive to temperature, particularly at high amino acid loadings on the resin. However, mass transfer rates for conditions where the intraparticle resistance is dominant are found to increase substantially as temperature is increased, with the effect being more pronounced for resins of higher degree of crosslinking. Intraparticle diffusivities are obtained from alkaline desorption experiments, while external film mass transfer coefficients in an agitated contactor are obtained from the rates of amino acid uptake from a dilute solution. Intraparticle diffusivities are strongly dependent on the hydration water of the resin and they increase substantially as temperature is increased.