In the present work, the adsorption of cephalosporin C and deacetylcephalosporin C on six different adsorbents has been studied. Two of the adsorbents were commercial Amberlite XAD-2 and Amberlite XAD-4, and the other four were their corresponding brominated and bromoethylated derived resins, respectively. The research was carried out by means of pulse experiments in a high-performance liquid chromatography (HPLC) system, and the corresponding chromatographic responses were analyzed using the moment theory. The results showed that the chemically modified XAD-2 resins enhanced the adsorption constant for cephalosporin C. Specially, brominated XAD-2 resin showed an increase in K-A of similar to 3 x with respect to the commercial adsorbent at 15 degrees C. In addition to the equilibrium and thermodynamic properties of the adsorption process, the effective pore diffusion coefficient, D-p, was also calculated. In all experimental conditions, the values of Dp were always larger for the modified resins, showing a consequent decrease in the internal mass transfer resistance of both cephalosporin C and deacetylcephalosporin C.