The kinetics of leaching of high-grade chalcopyrite (CuFeS2) concentrate (38-53 mu m) by the acidophilic thermophilic bacterium, Acidianus brierleyi, was studied at 65 degrees C and pH 1.2 in a batch stirred reactor. The adsorption of A. brierleyi cells between the sulfide surface and solution was attained within the first 20 min of exposure to the mineral, and the equilibrium adsorption data were correlated with the Langmuir isotherm. The bioleaching was markedly accelerated in the presence of A. brierleyi, and greater than 90% leaching of copper in the concentrate was achieved within 10 days. The chalcopyrite leaching with A brierleyi was found to take place with a direct - attack by adsorbed cells on the mineral surface, the chemical leaching of chalcopyrite by ferric iron being insignificant. Rate data collected under a wide variety of operating variables were analyzed to determine kinetic and stoichiometric parameters for the microbial chalcopyrite leaching.