The aim of this investigation was to determine the efficacy of chalcopyrite bioleaching using pure cultures of Acidithiobacillus ferrooxidans or Acidithiobacillus thiooxidans and a mixed culture composed of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. The experiments were carried out in shake flasks with [Fe2+] 4 g L-1 and S 1 g L-1 at pH 1.80, 130 rpm and 30 degrees C. Inocula of both iron-oxidizing bacteria were obtained from cultures with Fe2+ as the sole energy source, whereas Acidithiobacillus thiooxidans inoculum was taken from a culture growing on sulphur. Tests showed that the copper extraction in a mixed culture of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans was higher than in pure cultures. On the other hand, an important potential of Acidithiobacillus thiooxidans to leaching chalcopyrite was indicated. It can prevent jarosites accumulation on the substrate and allow further copper solubilization through the action of ferric ion. The selection of the suitable pH during the bioleaching processes would be important. (c) 2005 Elsevier Ltd. All rights reserved.