The simultaneous biosorption of three metal ions - chromium(VI), iron(III) and copper(II) - has been studied using R. arrhizus. The ability of the fungal biomass to bind three metals simultaneously is shown as a function of levels of metal concentration and ratios of metals. Since the initial biosorption rates, equilibrium and ultimate metal removal decreased with increasing concentrations of the other metal ions, the combined action of Cr(VI), Fe(III) and Cu(II) ions on R. arrhizus was generally found to be antagonistic. Although Cr(VI) ions were adsorbed selectively from the ternary metal mixtures, Fe(III) ions competed strongly with Cr(VI) ions to bind to active sites on the fungus.