A thermophilic culture specific to bioleaching chalcopyritic materials has been obtained from a typical chalcopyritic copper concentrate of the Spanish Pyritic Belt. This paper shows the effect of pulp density (w/v) on bioleaching culture capacity with respect to this copper concentrate. The results of the batch tests show that it is possible, operating at 10% of pulp density to attain copper extraction of 94% in 10 days and, at higher pulp densities (20%), to attain good copper extraction (80%) in only 14 days. In the same way, the culture has been amply tested with different chalcopyritic ores and copper concentrates. The results obtained with four of these materials, two refractory gold ores and two copper concentrates are also presented. These results show a varying and versatile bioleaching capacity of this bacterial culture. A model of bacterial attack of this culture to leach chalcopyrite is postulated. (C) 2002 Elsevier Science Ltd. All rights reserved.