Dehalococcoides strains are strictly anaerobic bacteria which can utilize chlorinated compounds in their energy metabolism. They utilize polychlorinated benzenes, phenols and dibenzodioxins as growth-supporting electron acceptors. Dehalococcoides are considered as "dechlorinated workers". They belong to obligate dehalorespiring bacteria and have a highly restricted lifestyle, deriving energy from reductive dehalogenation of haloaliphates or haloaromatics with hydrogen as the sole electron donor. Dehalococcoides are often maintained and studied in mixed cultures because they always have a slow growth rate and big difficulties in cultivation. From bioremediated herbicide/dioxin anaerobic cells in the frame of the cooperative project between VAST and EPA at pilot scale for detoxification of herbicide/dioxin contaminated soil in the former Da Nang military airbase, Dehalococcoides and other obligate anaerobic bacteria were enriched in an attempt. In the anaerobic medium 204, Dehalococcoides strains and other anaerobes grew in P1 and P5 enrichments containing 2,4-DCP and 2,4,5-T, respectively. Moreover, several different anaerobic bacteria which differed from morphology were detected in these enrichments. In addition, 100 percent of 2,4-DCP was reductively dehalogenated by these enrichments for 9 weeks. 80-100 percent of 2,4,5-T was also reductively dehalogenated by them for 12 weeks. This was the first finding in Vietnam about reductive dehalogenation of 2,4-DCP and 2,4,5-T by enrichment cultures driving to defind pathway and kinetics of reductive dehalogenation.