A study on the biosorption of toxic metals (copper, manganese, nickel and lead) by a species of Arthrobacter is presented. The equilibrium of the process was in all cases well described by the Langmuir isotherm. The highest values of specific uptake were 406 mg Mn/g, 148 mg Cu/g, 13 mg Ni/g and 130 mg Pb/g. Some factorial experiments were performed in order to investigate the effect of operating and cultural conditions on the equilibrium. Experimental results showed the influence of the biomass concentration on the specific uptake (mg of metal/g of biomass as dry weight). A comparison with results reported in the literature was made.