The catalytic influence of Sulfolobus metallicus in the bioleaching of pure chalcopyrite at 70° C and pH 1.5 was studied in shake flask experiments. In order to evaluate separately the influence of planktonic and attached cells on the catalytic process, in some experiments the microorganisms were prevented from reaching chalcopyrite surface by keeping them in a chamber separated by a 0.1 Millipore membrane. Leaching, which was conducted with a -80 # + 120# chalcopyrite sample, was characterized from monitoring Eh, pH, copper, ferrous and ferric ion concentration in solution. In addition, the concentration of different sulphur species dissolved in solution either in aerated-abiotic and aerobic - biotic conditions, was determined with HPLC. Maximum copper dissolution was reached in experiments where all the microorganisms could reach chalcopyrite. In experiments where microorganisms were maintained separated from the sulphide, the population of microorganisms still increased. However, in this case copper dissolution was only 50 % of the maximum reached when contact of microorganisms with chalcopyrite was allowed, similar to that obtained in aerobic-abiotic conditions. On the other hand, in aerobic-abiotic conditions there was formation of bisulfite (HSO3)-, bisulfate (HSO4)- and sulfate (SO4)2-, while in leaching experiments where microorganisms could reach chalcopyrite the formation of thiosulfate (S2O3)2- and sulfite (SO3)2- was additionally observed. It can be concluded that bioleaching of chalcopyrite in the presence of Sulfolobus metallicus is the result of the cooperative action of attached cells which catalize copper dissolution through formation of thiosulfate, sulfite and bisulfite, and planktonic cells which further oxidize these intermediate compound to bi-sulfate and sulfate.