Three ferrous-oxidising, acidophilic bacterial isolates oxidised Fe2+ when growing on yeast extract; one isolate but not the other two grew on ferrous sulphate as the only energy source. The isolates did not grow on either pyrite, sulphur or thiosulphate, but they grew on chalcopyrite and solubilize copper. They are mesophiles but can be adapted to grow at 38 degrees C and 45 degrees C. Their bioleaching activities at these temperatures were evaluated and compared.