The activation energies of Fe(III) and Pb(II) ions on Zoogloea ramigera and Fe(III), Cr(VI) and Ni(II) ions on Rhizopus arrhizus were determined using the Arrhenius equation. Batch adsorption kinetics was described by the Langmuir-Hinshelwood model. The applicability of the Langmuir-Hinshelwood model for the metal-microorganism systems was tested at different temperatures in the range 15-45 degrees C. With respect to the magnitude of the activation energy of biosorption, the dominant adsorption mechanism in the whole biosorption process was proposed for each metal-microorganism system. (C) 2000 Elsevier Science Ltd. All rights reserved.