Polished discs of a complex sulphide ore were leached with three lixiviants; a mixed culture of Thiobacillus ferrooxidans and Thio bacillus thiooxidans, Thiobacillus ferrooxidan alone, and ferric sulphate. At either one or two week intervals the discs were examined by scanning electron microscopy, and the amount of soluble metals released from the discs were determined. The mixed culture solubilized more Cu, Zn and Pb than did either ferric sulphate or T. ferrooxidans alone. However, no differ- ences were observed between the three treat- ments by scanning electron microscopy during the first 44 weeks. The minerals were attacked in the following order: pyrrhotite, cubanite, sphalerite, pyrite and chalcopyrite.