Biosorption of Ni(II) from aqueous solutions using Pseudomonas sp. and Staphylococcus xylosus cells was investigated under various experimental conditions for different pH values, biomass concentrations and contact times. The optimum pH value was determined to be 5.0 and 6.0 for Pseudomonas sp. and S. xylosus, respectively, and the optimum biomass concentration was 1.0 g L-1 for both microorganisms. Ni(II) biosorption was found to fit better to the Freundlich model and the maximum uptake capacity of Ni(II) was estimated to be 508 mg g(-1) for Pseudomonas sp. and much lower (89 mg g(-1)) for S. xylosus. Desorption experiments by treating biomass with 0.1 M HNO3 solution resulted to more than 87% recovery of the adsorbed nickel ions from Pseudomonas sp. and almost 98% from S. xylosus, indicating that nickel can be easily and quantitatively recovered from biomass, as well.