The pressure-jump method and the mixing method are applied to determine the adsorption-desorption mechanisms of alkali metal ions, basic amino acids, and lysozyme on the carboxymethyl (CM) Sephadex C-25. The adsorption-desorptions of both the alkali metal ions and the amino acids are accompanied by a conformational change of the Sephadex particle, which is the rate determining step. A lysozyme molecule is exchanged for several protons on the CM Sephadex surface, and the adsorption-desorption of the protein can be represented by a multistep ion-exchange mechanism.