Microbiol. influenced corrosion (MIC) of metals is generally assocd. with the existence of a biofilm. To simulate and monitor these processes a mobile test app. was developed offering the possibility to test simultaneously the resistance of different metallic materials. The biofilm development on metal surfaces and the corrosion resistance of metal samples were examd. on steel (St 37, 1.4301). The strongest attack on St 37 steel was obtained with a biogenic sulfide film at the metal surface as a result of the metab. of sulfate reducing bacteria being exposed to O2. A continuous change between anaerobic and aerobic conditions in the presence of sulfate reducing bacteria resulted in a maximal penetration of about 1 mm/yr in the case of St 37 steel. Under strict anaerobic conditions penetration amounted to 0.7 mm/yr. A microcalorimetric test was developed to det. microbial activity of biofilm samples. The test offers a certain advantage for measuring the efficiency of biocides. The concn. of a com. biocide had to be increased considerably to be effective.