Extensive corrosion of the Hamburg sewer network by biogenic H2SO4 has been obsd. A field study indicated thiobacilli of the species Thiobacillus neapolitanus, T. intermedius, T. novellus, and T. thiooxidans. A pos. correlation between the cell nos. of T. thiooxidans and the grade of corrosion was noted. The possible sources of S are the volatile compds. H2S, sulfite, methylmercaptan [74-93-1], Me2S [75-18-3], dimethylsulfide, and dithiabutane [624-92-0]. Biogenic concrete corrosion was simulated in a strictly controlled H2S breeding chamber. Differences among various concrete types were reproducibly demonstrated.