Biosorption of each of the ions Cr6+, Pb2+ and Cu2+ on Bacillus sp. in a batch stirred system was investigated and optimum conditions were determined. Then, the multi-metal ions, containing different concentrations of Cr6+, Pb2+ and Cu2+ ions together were prepared and partial competitive adsorptions of these mixtures were investigated at 27 degreesC and for the pH values of 4.0 and 7.0 that are the most frequently seen conditions in industrial waste waters. Parameters such as co-adsorption of metals to microorganism, combination, concentration and adsorption sequence affect the partial competitive adsorption. In conclusion, in the metal ions mixture, lead biosorption increases widely while chromium and copper biosorptions decrease in comparison with the biosorption of only one kind of metal ion. (C) 2002 Elsevier Science B.V. All rights reserved.