In in situ bioremediation demonstration at the Savannah River Site in Aiken, South Carolina, trichloroethyle degrading microorganisms were stimulated by delivering nutrients to the TCE-contaminated subsurface via horizontal injection wells. Microbial and chemical monitoring of groundwater from 12 vertical wells was used to examine the effects of methane and nutrient (nitrogen and phosphorus) dosing on the methanotrophic populations and on the potential of the subsurface microbial communities to degrade TCE. Densities of methanotrophs increased 3-5 orders of magnitude during the methane- and nutrient-injection phases; this increase coinclded with the higher methane levels observed in the monitoring wells. TCE degradation capacity, although not directly tied to methane concentration, responded to the methane injection, and responded more dramatically to the multiple-nutrient injection. tion. These results support the crucial role of methane, nitrogen, and phosphorus as amended nutrients in TCE bioremediation. The enhancing effects of nutrient dosing on microbial abundance and degradative potentials, coupled with increased chloride concentrations, provided multiple lines of evidence substantiating the effectiveness of this integrated in situ bioremediation process.