We investigated the replacement of NaCN with Acidithiobacillus ferrooxidans, in the flotation of a low-grade lead-zinc ore containing high amounts of pyrite. A. ferrooxidans were adapted to original ore, and its growth curves were monitored before and after adaptation. Because of its characteristics, the addition of original ore caused the bacterial cell count to increase in the culture medium and growth improved. The effect of the bacteria and their capability to depress pyrite were investigated in galena and sphalerite concentrates. Two models were then fitted to the sphalerite and pyrite recoveries. The results indicated that pyrite was significantly depressed in the both galena and sphalerite concentrates, using A. ferrooxidans like NaCN depressant. (C) 2011 Elsevier B.V. All rights reserved.