Dead Penicillium chrysogenum mycelium was used for the removal of three anionic dyes: acid orange 8 (AO8), acid blue 45 (AB45) and reactive orange 16 (RO16). The biomass surface was modified with polyethylenimine (PEI) and cross-linked with glutaraldehyde for enhanced anionic dye sorption. The sorption of dyes by both pristine and modified biomass was favored at lower pH, due to the electrostatic interactions between the dye anions and the protonated amine groups on the biomass. The effect of temperature over the range 30-70 degrees C on the sorption capacity was not significant. Compared to the pristine biomass, the maximum sorption capacity of the surface-modified biomass for AO8, AB45 and RO16 increased from 33, 18 and 25 mg/g, respectively to 352, 196 and 338 mg/g, respectively. Dye sorption using the pristine and modified biomass was well described by the Freundlich and Langmuir isotherm, respectively. FTIR analysis showed that PEI was grafted on the biomass surface via interactions with the amine groups on the pristine biomass. Regeneration of the PEI-modified biomass using AO8 as the adsorbate showed that the biomass could be used repeatedly up to seven cycles with negligible loss in dye removal efficiency. (C) 2007 Elsevier B.V. All rights reserved.