The biosorption of three divalent metal ions (lead, nickel and copper) in single component, binary and ternary systems has been studied using Rhizopus arrhizus, a filamentous fungus, in a continuous-flow stirred-tank contactor (CFST). For the prediction of the performance of CFST for mono and multi-component biosorption of heavy metal ions, a mathematical model based on mass balances for liquid and solid phases has been used. Initially mono-component biosorption was considered and the values of the forward and backward rate constants, K-1 and K-2, were calculated and were used for modelling of the multi-component biosorption in the CFST. The model generated concentration curves that compared favourably to experimental results. The relative capacities in the ternary metal mixtures were in the order Pb(II) > NI(II)> Cu(II), in agreement with the single and dual component data. (C) 2000 Elsevier Science Ltd. All rights reserved.