Saccharomyces cerevisiae, waste biomass originated from beer fermentation industry, was used to remove copper ion from aqueous solution. The biomass was modified by various chemical agents, including methanol, formaldehyde and glutaraldehyde in order to study the role played by various functional groups in the cell wall of S. cerevisiae in biosorption of copper. Esterification of carboxyl and methylation of amino groups present in the cell wall significantly decreased the biosorption capacity of copper, which suggests that both carboxylic and amine groups play an important role in biosorption of copper. However, glutaraldehyde-treated biomass almost retained the original biosorption capacity. (C) 2002 Elsevier Science Ltd. All rights reserved.