The biosorption of nickel(II) ions by deactivated protonated yeast was investigated with respect to the initial pH and initial metal ion concentration. The kinetics of sorption was also followed based on the amounts of metal sorbed at various time intervals for different yeast doses. The equilibrium data could be fitted by the Langmuir isotherm model. The adsorption capacity was pH dependent with a maximum value of 11.4 mg/g at a pH of 6.75. The nickel(II) ion uptake was pseudo-second order with respect to metal concentration and was yeast dose dependent. The rate constant, the equilibrium sorption capacity and the initial sorption rate are reported. (C) 2002 Elsevier Science Ltd. All rights reserved.