The bacteria belonging to the class Dehalococcoidia , due to their ability to dehalogenate chlorinated compounds, are of much interest for bioremediation of contaminated sites. We report here comparative analyses on different genes/proteins from the genomes of members of the class Dehalococcoidia . These studies have identified numerous novel molecular markers in the forms of conserved signature indels (CSIs) in broadly distributed proteins and conserved signature genes/proteins (CSPs), which are uniquely found in members of the class Dehalococcoidia , but except for an isolated exception, they are not found in other sequenced bacterial genomes. Of these molecular markers, nine CSIs in divergent proteins and 19 CSPs are specific for members of the genera Dehalococcoides and Dehalogenimonas , providing potential molecular markers for the bacterial class Dehalococcoidia . Additionally, four CSIs in divergent proteins and 28 CSPs are only found in all members of the genus Dehalococcoides for which genome sequences are available, but they are absent in Dehalogenimonas lykanthroporepellens and in other bacteria. The gene sequences of several of these CSPs exhibiting specificity for the genus Dehalococcoides or the class Dehalococcoidia are highly conserved and PCR primers based upon them provide a novel means for identification of other related bacteria. Two other CSIs identified in this study in the SecD and aspartate carbomyltransferase proteins weakly support an affiliation of the class Dehalococcoidia with the other members of the phylum Chloroflexi.