In this study, simultaneous biosorption of Gemazol Turquoise Blue-G reactive dye anions and copper(II) cations to dried sugar beet pulp, an agricultural solid waste by-product, from binary mixtures was studied and compared with single dye and metal ion situation in a batch stirred system. The effects of pH and single and dual component concentrations on the equilibrium uptake of each component, both singly and in mixture were investigated. The working pH value for the biosorption of single Gernazol Turquoise Blue-G dye and single copper(II) was determined as 2.0 and 4.0, respectively. The equilibrium uptake of each component increased with increasing its initial concentration up to 750 mg l(-1) for dye and up to 200 mg l(-1) for copper(II) ions for both pH values. The presence of increasing concentrations of copper(II) ions increased the equilibrium uptake of dye anions while the adding of increasing concentrations of dye diminished the copper(II) ion uptake for both pH values studied. This situation showed the synergistic effect of copper(II) cations on dye biosorption and the antagonistic effect of dye anions on copper(II) biosorption. Adsorption isotherms were developed for single-dye, single copper(II) and dual-dye-copper(II) ion systems at these two pH values and expressed by the mono-component Langmuir model and multi-component synergistic and antagonistic Langmuir models and model parameters were estimated by the non-linear regression. (c) 2006 Elsevier B.V. All rights reserved.