A study on the microbial diversity in 2 U mine waste heaps revealed that many different physiol. groups of microorganisms occurred. The acidophilic thiobacilli Thiobacillus ferrooxidans and Thiobacillus thiooxidans were the dominant microorganisms in a U mine waste heap with a mean pH of 4. Moderately acidophilic thiobacilli dominated in a 2nd heap with carbonaceous material and a mean pH of 6. Tetra- and pentathionate were detected in carbonaceous ore samples. Polythionates are the main products in the case of chem. pyrite oxidn. expts. at pH 7.9, explaining the source of substrate for the moderately acidophilic thiobacilli. In the case of pyrite oxidn. at pH 1.9 more than 90% of the pyritic S was completely oxidized to sulfate, together with 10% of elemental S and traces of polythionates. Elemental S is a suitable substrate for Thiobacillus thiooxidans. For remediation purposes the action of inhibitory substances on bacterial leaching was tested. An efficient inhibition of the acidophilic leaching bacteria Thiobacillus ferrooxidans, Thiobacillus thiooxidans, and Leptospirillum ferrooxidans was achieved by Na dodecylsulfate (SDS), CaF2, concrete, and CaCO3. The latter 3 agents were suitable for a long-term protection of mine waste resulting from measurements of microbial activity, cell count, and metal solubilization. Dissolved SDS allows for a temporary treatment.