While chitosan biopolymer from crustacean shells is recognized as a good adsorbent of metals from aqueous solutions, chemical cross-linking is necessary to avoid biopolymer solubility in acidic medium. Adsorption of chromium onto cross-linked chitosan is realized by means of analysis of pH influence, particle size, adsorbent weight, concentration and oxidation state of metal. Concentrations of chromium in solution are determined by Flame atomic absorption spectrometry and colorimetric method with diphenylcarbazide. Optimum pH of adsorption is 4.0 while chromium(VI) is partially reduced in the range pH <= 3.0. The lower affinity of chitosan by chromium(III), 6 mg/g, differs with the high capacity developed with chromium(VI), 215 mg/g, due to highly protonated active sites in the acidic range of pH. Equilibrium data fit to both Langmuir and Freundlich isotherms. (C) 2004 Elsevier B.V. All rights reserved.