The US Department of Energy, Office of Technology Development, has supported a field-scale in situ demonstration of trichloroethylene (TCE) bioremediation at the Westinghouse Savannah River Site (WSRS). Several methods were used to examine the influence of nitrogen and phosphorus species on TCE degradation during methane (CH4) injection into contaminated sediments. Laboratory experiments using WSRS ground water revealed that the rate of acetate incorporation into microbial lipids was stimulated when triethyl-phosphate (TEP) or nitrous oxide (N2O) was added. The trend was : CH4 + N2O > CH4 + TEP > CH4 + N2O + TEP > CH4 alone. The degree of stimulation of C-14-TCE mineralization in ground water incubated for 30 d in the laboratory with added methane and nutrients increased in the order : OP = TEP > NH3 + TEP = NH3 > N2O (OP, orthophosphate; NH3, ammonia). Monitoring of WSRS ground water revealed significant differences among sampling wells over time in nutrient concentrations, nitrogen uptake, and urease activity during operations of the bioremediation demonstration. In the field, the addition of TEP + N2O to the pulsed injection of CH4 resulted in dramatic stimulation of TCE-degrading potentials observed in ground water enrichments. The potential to mineralize C-14-TCE in ground water enriched with nutrients in the laboratory increased from <50% of the samples taken during injection of methane in the field to >90% of the samples taken during the injection of CH4 + TEP + N2O treatment. These results demonstrated the dramatic impacts of nitrogen and phosphorus supplements during the in situ bioremediation of chlorinated solvents.