Both, the employment of leaching bacteria for metal winning as well as the mitigation of bioleaching processes at AMD/ARD sites, require reliable monitoring methods for assessing bacterial activities. Therefore, we have developed a robust and rapid test system combining two sensitive analytical techniques: quantification of heat evolution by microcalorimetry and determination of all relevant inorganic sulfur species by chromatographic methods (IC and HPLC). Generally, only about 1 g of sample is sufficient for a complete analysis. The combined test has been applied to various leaching biotopes such as bioreactors, columns, heaps and natural sites. The bacterial activity of diverse sulfidic materials such as lignite and coal wastes, pure metal sulfides and complex ores has been investigated. In our labs, microcalorimetry can be performed in the range of 5 to 80 °C, covering most of the temperature spectrum of leaching bacteria. Hence, the heat evolution values of samples as a direct measure for calculating leaching rates can be obtained at nearly all relevant in situ temperatures. The combination with sulfur species determination results in additional information on leaching mechanisms (thiosulfate or polysulfide pathway) and general leaching performance (e. g. accumulation of sulfur intermediates).