Vinyl chloride (VC), a known human carcinogen, neurotoxin and common groundwater contaminant, represents a serious threat to public health if VC contaminates drinking water source zones. The presence and activity of VC-degrading bacteria at a contaminated site is a crucial line of evidence for demonstrating natural attenuation and a subsequent reduction of risk to human health. Because VC-degrading bacteria appear to be a specialized, non-ubiquitous subset of the ubiquitous ethene-degrading bacteria, there is currently no sequence-based method to distinguish an ethene-degrading bacterium from a VC-degrading bacterium. This is a serious shortcoming for site assessment and bioremediation studies. To alleviate this shortcoming and enhance our ability to compete for external research support, we propose to sequence VC and ethene biodegradation genes from several VC-degrading and solely ethene-degrading bacteria. This work will generate a gene database to facilitate molecular probe design and will shed light on possible VC acclimation mechanisms.