A process of fully competitive biosorption of Cr(VI) and Fe(III) ions to C. vulgaris and R. arrhizus from multi-component systems is described and compared to single metal ion situations in solution. The effects of the presence of Cr(VI) and Fe(III) ions together on the biosorption of Cr(VI) and Fe(III) ions were investigated in terms of initial rates of biosorption and equilibrium isotherms. Since initial biosorption rates and equilibrium metal removal decreased with increasing concentrations of the other metal ion, the combined action of Cr(VI) and Fe(III) ions on C. vulgaris and R. arrhizus was generally found to be antagonistic. In the single ion situation, the adsorption isotherms were developed for optimum conditions and adsorption equilibrium data fitted both the non-competitive Langmuir and Freundlich models. For the multi-component adsorption equilibrium, competitive adsorption isotherms were also developed. The competitive Freundlich model for binary metal mixtures was satisfactory for most adsorption equilibrium data of Cr(VI) and Fe(III) ions on C. vulgaris, while the competitive Langmuir model and the modified Langmuir model were used successfully to characterize competitive adsorption of Cr(VI) and Fe(III) ions from two component systems by R. arrhizus.