Enargite (Cu3AsS4) was leached at 70 degrees C by Sulfolobus BC in shake-flasks. The highest copper dissolution (52% after 550 h of leaching) was obtained with bacteria and 1 g l(-1) ferric ion. In the absence of ferric ion, Sulfolobus BC catalyzes the bioleaching of enargite through a direct mechanism after adhesion onto the mineral surface. In ferric bioleaching, arsenic precipitated as ferric arsenate and arsenic remained associated to the solid residues, preventing the presence of a high dissolved arsenic concentration in the leaching solution. About 90% inhibition of bacterial growth rate and activity was observed for dissolved arsenic concentrations above 600 mg l(-1) for As(III) and above 1000 mg l(-1) for As(V). Arsenic-bearing copper ores and concentrates could be leached by Sulfolobus BC in the presence of ferric iron due to the favourable precipitation of arsenic ion as ferric arsenate, avoiding significant bacterial inhibition.