In percolator expts. with a pyritic ore and the mesophilic Thiobacillus ferrooxidans as leaching bacterium the metal sulfide oxidn. was accurately quantified by measuring calorimetrically the thermal power of ore samples within 1-2 h in batch expts. Furthermore, the temp. dependence, i. e. the activation energy, of this leaching reaction was also calorimetrically detd. The data show that microcalorimetry might be a suitable short-time method for the quantification of the mobilization rates of heavy metal ions in natural leaching biotopes.