In this study, the Box-Behnken design matrix and response surface methodology (RSM) have been applied to design the experiments to evaluate the interactive effects of three most important operating variables: pH (2.0-6.0), temperature (25-40 C) and initial concentration of metal ions (10.0-60.0mg/L) on biosorption of Cr (VI), Ni (II) and Zn (II) ions with immobilized bacterial strain Bacillus brevis. The total 17 experiments were conducted in the present study towards the construction of a quadratic model. Independent variables have significant value 0.0001 which indicates the importance of these variables in the biosorption process. Values of "Prob>F" less than 0.0500 indicate that model terms are significant for the biosorption of Cr (VI), Ni (II) and Zn (II) ions. The regression equation coefficients were calculated and the data fitted to a second-order polynomial equation for removal of Cr (VI), Ni (II) and Zn (II) ions with immobilized bacterial strains B. brevis. (C) 2008 Published by Elsevier B.V.