The applicability of microcalorimetry in the rapid evaluation of bacterial ore leaching was investigated. Thermograms were recorded of Thiobacillus (T.) ferrooxidans, T. thiooxidans, T. intermedius, T. novellus, T. neapolitanus, Leptospirillum ferrooxidans, and Sulfolobus brierleyi during growth on Fe(II), S, and thiosulfate. The combination of thermograms with chem. and biol. anal. demonstrated that thiosulfate oxidn. proceeds via 3 steps. The thermograms were reproducible and strain-specific. Thus, a rapid characterization of unknown strains is possible. Microcalorimetry enables the detection of microbial growth and metab. before chem. anal. The high sensitivity enables the investigation of the degradability of S, pyrite, and ores.