There is a need to develop technologies that can remove toxic heavy metal ions found in wastewaters. Microorganisms are known to remove heavy metal ions from water. In this study the potential of the fungus Aspergillus niger to remove lead, cadmium, copper and nickel ions was evaluated. A. niger biomass pretreated by boiling in 0.1N NaOH solution for 15 min exhibited higher lead, cadmium and copper removal capacities than did live biomass. Live A. niger biomass was found to be more effective in the removal of nickel than biomass which had been boiled in 0.1N NaOH solution for 15 min. The pH of the solution strongly affected the degree of biosorption of heavy metal ions on biomass pretreated by boiling in 0.1N NaOH solution. Biosorption of metal ions was inhibited at pH 3.0, and sharply increased when the pH of the solution was increased to 4.0. Biosorption of lead and cadmium reached equilibrium in 5 h, and equilibrium was reached in 6 and 8 h for copper and nickel, respectively. Biosorption of heavy metals on pretreated biomass followed the Freundlich and Langmuir adsorption models, except at pH 4.0 for lead, cadmium and copper and at pH 5.0 for nickel. The removal of lead, cadmium and copper ions by pretreated A. niger biomass was higher than the removal obtained using granular activated carbon (F-400). Removals of lead, cadmium and copper ions were lower when present together in solution in comparison with the removals obtained when these metal ions were present individually in solution. The biosorbed metal ions were effectively eluted by 0.05N HNO₃ solution. After eluting, the biosorbed metal ions biomass was regenerated by washing with deionized water and then contacted with a solution containing 0.1M of Ca²⁺, Mg²⁺ and K⁺ ions before further adsorption tests. The pretreated A. niger biomass could be used for five cycles of biosorption – elution of biosorbed ion – regeneration of biomass. This research showed that fungal biosorption had a potential to be used in the removal of heavy metal ions from wastewaters.