This study reports the possibility of enhancing the reactive dye biosorption capacity of Corynebacterium glutamicum via its cross-linking with polyethylenimine (PEI). The amine groups in the cell wall of C glutamicum were found to electrostatically interact with reactive dye anions. Thus, cross-linking the biomass with PEI enhanced the primary and secondary amine groups, thereby increased the biosorption of reactive dye. The pH edge experiments revealed that acidic conditions, due to protonation of the amine groups, were found to favor Reactive Red 4 (RR 4) biosorption. According to the Langmuir model, the PEI-modified C. glutamicum recorded a maximum RR 4 uptake capacity of 485.1 mg/g compared to 171.9 mg/ g of the raw C glutamicum. The kinetic experiments revealed that chemical modification decreased the rate of biosorption. Desorption was successful at pH 9, with the biomass successfully regenerated and reused over four cycles. (c) 2008 Elsevier Ltd. All rights reserved.