Lyophilized biomass of a Pseudomonas soil isolate adsorbed thorium (IV) (430 mg g(-1) dry wt) optimally at pH 4, with 91% of equilibrium loading being reached in 1 min. Equilibrium metal sorption showing conformity to Langmuir isotherm model suggested a monolayered thorium binding. Thorium binding remained unaffected or slightly affected (< 20% inhibition) in presence of equimolar (430 muM) concentration of several interfering ions except Fe3+ (40% inhibition). More than 90% of loaded thorium could be recovered using 1 M CaCO3, though mineral acids and Na2CO3 were also effective.