Metal sulfides are degraded via thiosulfate (pyrite) or via polysulfides and sulfur (sphalerite, galena, chalcopyrite) by leaching bacteria. The attack on the crystal lattice is either effected by only iron(III) ions or by iron(III) ions and protons, resp. Consequently, different endproducts are formed. For a control of ARD-processes, these reactions need to be known to regulate them. Expts. in percolators up to 65 m3 with inorg. compds. like fluoride, concrete, or SDS resulted in differently lasting inhibition. Microcalorimetric measurements of microbial leach activity allow monitoring of these effects with respect to active bacterial cells, and, in addn., the amt. or rate of dissolved metal sulfide allowing prediction of possible endangerment by ARD.