As a consequence of industrial activity, enormous quantities of metals are accumulating in waste products and spent materials all over the world. An inadequate disposal of these materials could cause hazardous environmental problems if their substantial amounts of toxic metals are mobilised and reach soils and groundwater. Besides, wastewaters containing different metals at concentrations high enough to need an adequate treatment, are generated by many industrial processes. Biotechnology can be utilized in clean-up programmes to reduce the possibility of contaminate the environment or to recover valuable metals. Different microbial processes have been used for either solubilisation or immobilisation of toxic metal ions. Many of these processes are based on the activity of sulphur and iron-oxidising bacteria which have been used successfully for metal leaching not only from low-grade ores and concentrates but also from solid waste. On the other hand, sulphate-reducing bacteria are able to immobilise metals through their metabolic activity. In this paper we present an up date of these methods and also some of our results in the recovery of heavy metals from nickel-cadmium batteries, vanadium catalysts and chromium-contaminated residues by microbial processes.