The biosorption of 241Am from solution by a fungus-Rhizopus Arrihizus (R. arrihizus), and the effect of experimental conditions on the adsorption were investigated. The preliminary results showed that the biosorption of 241Am by R. arrihizus is very efficient. An average of more than 99% of the total 241Am was removed by R. arrihizus of 1.3 g/l (dry weight) from 241Am solutions of 5.6-111 MBq/l (44.3-877.2 microg/l) (C0), with adsorption capacities (W) of 4.2-79.4 MBq/g biomass (dry weight) (33.2-627.5 microg/g). The biosorption equilibrium was achieved within 1 h and the optimum pH ranged from 1 to 3. No significant differences in 241Am biosorption were observed at 10-45 degrees C, or in solutions containing Au3+ or Ag+, even 2,000 times above 241Am concentration. The relationship between concentrations and adsorption capacities of 241Am indicated that the 241Am biosorption by R. arrihizus obeys the Freundlich adsorption equation.