PCBs are persistent organic pollutants which have entered the environment through both use and disposal. The environmental dissemination of PCBs is complex and nearly global in scale, although their production was banned in the 80’s. Nowadays, specific bacterial species were shown to degrade these compounds by attacking the bond between the aromatic core and the flanking chlorine atoms. This anaerobic dechlorination process could be a possible way for environmental bioremediation. Nevertheless, at present time, little is known about the diversity of the bacterial guild and enzymes involved in the process. In this context, anaerobic microcosms were inoculated with PCB-contaminated sediments collected from a water channel leaving a former chemical factory (Strazske, Slovak Republic). Total RNA and DNA were extracted after six months of continuous growth. The first goal was to identify the members of the dechlorinating bacterial guild, as well as identifying the enzymes which were involved in the reductive dehalogenation of the PCBs. A second goal was to identify environmental variables that influence the biological removal of PCBs in the contaminated sites. The anaerobic conditions imposed to the microcosms resulted in the enrichment of putative PCB dechlorinators (Dehalococcoides sp. as well as members of the Chloroflexi class). T-RFLP analysis of the initial bacterial communities and bacterial consortia in microcosms showed a clear shift in their respective compositions. Two microcosms samples are currently being analyzed in details using a cloning-sequencing strategy, leading to a sequence analysis and the construction of phylogenetic trees. The analysis of the PCB congeners present in the microcosms is currently under way. In parallel, a comprehensive list of all dehalogenase sequences found in databases was produced. Based on these sequences, new sets of degenerated primers were designed for the detection of putative genes involved in biodegradation of highly chlorinated PCBs.