Response surface methodology was applied to optimize the removal efficiency of Ni(II). Pinus sylvestris ovulate cones were used in this study. A 2(3) full-factorial central composite design was employed for experimental design and analysis of the results. The initial Ni(II) concentration (10-30 mg/l), pH (2.5-6.5) and biomass concentration (5-25 g/l) were the critical components of the removal optimized. The optimum pH, m (biomass concentration) and C-0 (initial Ni(II) concentration) were found to be 6.17. 18.8 g/l and 11.175 mg/l, respectively. Under these conditions, removal efficiency of Ni(II) was 99.91%. (c) 2005 Published by Elsevier Ltd.