The performance of 5-L laboratory bubbling columns in the biooxidation of a Chilean gold concentrate by Thiobacillus ferrooxidans was evaluated at pulp densities in the range of 6 to 24 % w/v and aeration rates of 3.0 to 4.5 vvm at pH 2.4 and 33°C. The concentrate contained 42 g gold/t, 41% enargite and 43% pyrite. Cell growth in the liquid and solid phases was observed only during the first days of operation. Growth was accompanied by a sustained solubilisation of Cu, Fe and As, and by a rapid increase in Eh from 400 to 610 mV. After this period, growth on the mineral surface stopped for reasons that are not apparent at this time. From then on, only a slight increase in the suspended population occurred. Nevertheless, the oxidative activity persisted throughout the 24-day period of each rtm. The highest rates of leaching were at 3.0 vvm and 24% solids. The results show a good performance of the columns and confirm the refractory nature of the enargite-pyrite concentrate.