The aim of this research project was to exploit the potential of thermophilic microorganisms for the degradation of xenobiotic compounds under conditions, which occur in many waste streams of production plants, that are so far considered not to be treatable biologically. For the purpose, thermophilic microorganisms were enriched, the degradation pathways were elucidated and the relevant enzymes in the degradation pathways were isolated and characterized. The usefulness of the newly isolated microorganisms in the solution of environmental problems was tested. In environmental samples a variety of new microorganisms with the potential for the degradation of environmental pollutants have been discovered. Under aerobic conditions, in the temperature range up to 75 C, several thermophilic bacilli have been isolated showing degradation of alkanes, phenols, cresols, chlorophenols, benzoate, naphthalene, biphenyl and different pyrethroids. Under anaerobic conditions reductive dehalogenation of tetrachloroethene to dichloroethene via trichloroethene at 60 C and the dechlorination of 3-chlorobenzoate to benzoate, as well as the degradation of benzoate and phenol, were observed. This project has shown that there exists a vast potential of thermophilic microorganisms in nature, which have the ability to degrade environmental pollutants at temperatures between 55 C and 75 C. For all major classes of compounds, as least one example of thermophilic degradation was found. These results should encourage a continuing search for other not yet discovered microorganisms. These organisms can help to degrade especially those compounds that are difficult to degrade at lower temperatures due to solubility and bioavailability problems. In order to implement a technology using the newly isolated microorganisms, we are now looking for companies that produce polluted hot waste waters.