BACKGROUND: Agro-waste materials can be used as biosorbents of heavy metals in aqueous solution. However, it is necessary to further study the contribution of agro-waste materials components (i.e. hemicelluloses, cellulose, and lignin) to the heavy metal ions removal from aqueous solution to better understand the biosorption mechanism, and also based on the biosorbents main components, to predict their potential to remove heavy metals. RESULTS: Cellulose is contained in major proportion (greater than 46%) in the agro-waste materials reported herein compared with hemicelluloses (from 12% to 26%), lignin (varying from 3% to 10%), and other compounds (22% to 30%) that were removed after the neutral detergent fiber procedure. The identified functional groups in agro-waste materials and their fractions included hydroxyl, carboxyl, and nitrogen-containing compounds. Lignin contributed in higher proportion than hemicelluloses to Cr (III) adsorption capacity in both sorghum straw and oats straw. On the other hand lignin was the main fraction responsible for Cr (III) adsorption in agave bagasse. CONCLUSION: Hemicelluloses and lignin were the main contributors to Cr (III) removal from aqueous solution, and cellulose contained in the agro-waste adsorbents studied did not seem to participate. (C) 2009 Society of Chemical Industry